I'm hoping y'all can help me out, lots of text

I have a 97 F250HD 4x4 E4OD with 340k miles

About 2 years ago I had the transmission rebuilt and the TC replaced. I honestly don't remember the exact symptoms but I know I was able to drive it in. After this I ended up taking it back a couple times for hard shifting but the issue seemed to eventually be resolved.

A year ago (110 degree summer perhaps a factor): transmission goes into limp mode - generally this is triggered by coming to a complete stop (ex at a red light) and then taking off again. The OD light would flash and the code was something equating to slippage. I ran through everything and realized the transmission was way overfilled. I'd never added fluid but also never paid much attention other than checking that the plastic end of the dipstick was wet. I drained probably over 3 quarts, till it read correctly on the dipstick, and once again it drove fine. Have had a gauge installed for entire time I've owned the truck, only ever hit 220 towing, otherwise 205 or below.

5 months ago: The shift points become really high, OD flashing, again a code about slippage. I ran through a variety of things first, replacing VSS, checking electrical connections (found connection to solenoid pack full of water), checking for frayed wires, etc to no avail. I left it parked for a while and drove another vehicle, only taking it around the block to warm up every other week. Occasionally it would start off fine, shifting perfectly all the way up to 4th and OD, but eventually it would always end up requiring high RPMs to get to 2nd, and usually 3rd being unattainable.

I took it to my parent's who have a nice shop and pulled the transmission out. No valves stuck, all solenoids seemed to be working, no hard parts damage, fluid was nice and clean. The accumulator body has a noise which sounds like a loose spring sliding around inside, I'm not sure if this is normal. Also, There was some gunk on the magnet (maybe a teaspoon of fine shavings) and the torque converter rattled when tipped side to side. I went ahead and replaced the TC and while I had everything out inspected and rewraped the transmission related wire looms under the truck.

The current state is this: no gear past 2nd, but reverse and low speeds otherwise seem to be functioning normally. If I put it in neutral and rev the engine to 2500+ RPM I can get the OD light to flash with P0500. I've already replaced the VSS sensor once and went over the wiring and found no obvious signs of damage. The speedometer seems to work, and with an Innova reader plugged into the OBDII port the live reading for speed seems reasonable/correct. I took the drain plug out of the rear differential and there was a chip of metal on it. The plan is to bust it open next weekend to inspect because it's been 80k miles since last change anyways.

Does anyone have any experience with this type of issue, or suggestions for things to check?

Suspects I have bouncing around right now include:

• Some electrical problem with PCM, ABS module, or speedo cluster
• MLPSensor - I reassembled this in park but saw a post about being in neutral, could this be a problem?
• Short or disconnect in harness
• Is loose spring sound correct for accumulator body?

thanks


Also, this post seems related to my problem, but no follow up has ever been posted