Hey guys, I've been troubleshooting this 2002 7.3 for 2 months now. After some improvements and a lot of figuring out what it's NOT, The power loss is now mostly evident at mid to high speeds. I can't accelerate past 84mph on flat highway, I can barely maintain 47mph up a hill on a highway (empty load), and it takes a good 10 seconds after merging from an on ramp to finish accelerating up to highway speed. Here is some background down to where I'm at:

How it came when I bought it in June with 230,000 miles:
2002 F250 7.3L diesel Lariat 4 door 6.5' bed; aftermarket intake, 6"lift, 37" mudding tires,

Original Symptoms:
Hard start cold and sometimes no start hot; low power and acceleration, especially at medium to high speeds or higher RPMs, couldn't accelerate past 72 ish MPH on level roads; twice I got the “injection pressure not controllable” check engine code – one of the times while driving that resulted in almost no power, but I pulled over, let the engine sit, cleared the code, turned it back on, and got home fine; fuel pressure was over 100psi with new pump on (engine running or off) and dropped to mid 50s with pump off (and engine off),

Things I had a shop do to address low power issue:
Run cylinder contribution test - 3&5 failing intermittently with low temperature while #1 read a good temperature and #7 had a medium temperature, replaced all passenger side injectors & glow plugs & valve cover gasket, replaced LPR & ICP sensor, replaced spring and plunger in fuel pressure regulator (was still high after that and that's when I clipped the spring). Had an expert shop diagnose it after replacing only the 3&5 injectors, and the guy said that fuel pressure was really high, but that shouldn't be causing the low power - do a compression test on the passenger side cylinders, and if they show good compression, then replace the 1&7 cylinders and that should fix it. I went forward with replacing the 1&7 cylinders to see if that would work and did the compression test after that didn't fix the issue (compression looked fine).

Things I did to address low power issue:
Checked oil level to ensure it was in spec, installed new CPS (purple one from amazon that was highly recommended), installed new fuel filter, installed new fuel pump, installed fuel pressure gauge, used fuel injector cleaning additive in fuel (Lucas brand), checked fuel screens in tank (looked super clean but I replaced them anyway), blew compressed air through fuel return line to ensure it wasn't clogged and removed spring and plunger from fuel pressure regulator to ensure fuel could flow freely back to tank (pressure held at 0 as expected when that was done), clipped fuel pressure regulator spring to lower pressure (was still high after shop swapped parts), cleaned air filter and replaced broken air filter restriction gauge which reads almost nothing now, added Hot Shot's Stiction Eliminator to oil and drove for over an hour before changing oil (& filter) and adding Archoil AR9100 oil additive post oil change, did a cold compression test to all 4 passenger side cylinders and they all read 350psi, deadheaded HPOP and it read 3400psi, hooked up compressed air to both sides of HP oil system and found one leak at ICP (post shop replacing it) so I changed the O-ring on it and had no leaks after that (haven't been able to get it started again after making that fix to see if it will run better)

Here's the latest update from today after hooking up and logging drives in FORScan:
-All gauge measurements of HPO pressure were pretty consistent with PID ICP output, so I'm going to assume that the ICP is good.
-All start-ups only took about 3 seconds and without help of camaro jumper cables => starter is likely good, and the gear drive on the HPOP is also likely sufficiently tight.
-Battery had a voltage of 12.7+ V at the end of a ~30 minute drive and held at 13.8V to 14V while being charged by the alternator => alternator is likely good (not that that was a possible explanation for symptoms).
-Without assist of jumper cable and a camaro, the batter voltage held at around 10.9V while cold cranking and only momentarily dropped to 10.3 at the onset of the crank. => battery appears to be good.
-At a steady 3000 RPM, I was able to hold almost 3000psi on ICP with IPR DC at about 51%. At longest duration of WOT, IPR never went above 55. I'm assuming that means that my HPOP is good and that my IPR is good.
-I did a buzz test on the injectors and they all buzzed, so I'm assuming that means that all electronics and wires going from IDM to injectors are good (right?)
-EBP read about 15psi at idle and up to 52psi at ~3000RPM WOT, => I don't know if that's normal, but I think it should at least mean that my EBPS is good and that the tube isn't clogged, right?
-While kept in first gear, at 3000 RPM WOT I got about 22psi of turbo boost => turbo and piping appears to be functioning properly
-EGT Pyrometer held at 700 deg F on the highway when the truck had been warmed up and working hard => I believe that's a good sign.
-I checked the HPOP reservoir before the first drive and between drives, and it always looked topped off. Additionally, LPOP pressure on dash remained steady => LPOP seems to be delivering enough oil to HPOP without significant leaks, drainage, or blockage.
-FUELPW was 0.6 while cranking, high 1's to low 5s while idling and through most driving conditions, between 0.6 & 2 while decelerating => not sure if that's good or bad, but it at least seems to be cycling in a controlled manner. There does not seem to be much of a correlation between amount of throttle applied and length of FUELPW other that it's under 2 when decelerating.
-Throttle Position Rate stayed at 0 the entire time, and Throttle Mode stayed "PT" the entire time => not sure if that's an issue
-While cold idling, ICP was 750-900 while IPR was 40-42% => seems a little high to me for both. For the cold run, Fuel pressure was idling at 70+, then on the highway WOT would drop down to 60+ => maybe the truck was trying to make high ICP to balance out high fuel pressure?
-While idling warm on that same first run with that same fuel pressure, IPR would be 4.7 and ICP high 500s to mid 600s => again, ICP seems a bit high.
-After several iterates of removing, clipping, and re-insterting the FPR spring, driving, seeing improvement, and repeating, the fuel pressure on my last drive was about 62psi at idle and as low as 45psi WOT on the highway. After that, the warm idle measurements were IPR: high 4s to mid 5s and ICP: 460 to ~550psi - still seems like it might still be a bit high.
-Power on first run with 70+psi idle: significant performance increase over previous driving, BUT still a huge lack of power. Couldn't accelerate past ~75mph on flat highway, and struggled to maintain 45mph with overdrive off up a steep highway hill. Struggled to pick up speed on the on-ramp.
-Power on final run with ~62psi idle: still better performance over first run, but still not what I would think to be normal. Accelerated only up to 84mph on flat highway; struggled to maintain ~47mph on that same hill, and still needing at least 10 extra seconds on the highway to reach highway speeds after merging from on-ramp. I understand that big tires and a 6" lift will detract some power, but it can't explain THAT much power loss, right?
-The only inadvertent idle while stalling occurred at the very end of the last drive => I'm not sure what to make of that. It would previously inadvertently stall while idling, usually while the engine is warm. Today, it stalled when I pulled partially into the driveway and placed it in reverse to straighten out - then stall.

After clearing codes and doing the final run (30+ minutes), I did not have a "check engine" light, but FORScan still read the following codes:
No codes on ODB2
B1352 - Ignition key in circuit fault (is this because I took out the piece that makes the car beep when the key is in the ignition and the ignition in "off"?)
P1000 - On-Board Diagnostic (OBD) Systems Readiness Test Not Complete (sounds like this is not an indicator of a problem, but that it still might be)
P0470 - Exhaust Back Pressure sensor circuit malfunction (this is one I don't understand because the EBPS seemed to be working on the oscilloscope)
P1876 - Transfer Case 2-Wheel Drive Solenoid Circuit Open Or Short To Ground (not sure what to make of that one)

Questions:
1) Was my assumption about the meaning of a successful buzz test correct?
2) a) Can I assume that the EBPS is functioning as designed? b) are those normal readings?
3) Does the FUELPW behavior indicate any issues?
4) Should I continue to lower my fuel pressure to see if the performance still gets better? I don't want to cut it too low. How low should it get before I start worrying that it's too low? I've heard anywhere from mid 40s to mid 50s is normal, but idk if that's idling or WOT.
5) What might that last idling stall be an indicator of given the other readings?
6) Given the above indications, what's the next thing I should be checking/looking for?

Thanks, guys! Codes are attached in .txt , runs are logged in .xlsx