Diesel Bombers - 1994 6.5TD DTC 36 Question

Hi. I am brand new to this forum and this is my first diesel, so please forgive newbie questions. I have searched online and found mixed results. 3 weeks ago I bought a 1994 C3500 Crew Cab Dually with the 6.5TD with 121,000 miles on it. Driving it home, I noticed the SES light coming on with acceleration over 1,400 - 1,500 RPM, and the light would go out with deceleration. It would stay on steady on the Interstate and would stumble under hard acceleration. Also, maybe 3 or 4 times, with the truck sitting idling either warming up or cooling down, I would hear a bang/pop, and one small puff of grey/back smoke roll out the exhaust. One and ONLY one pop and puff. It has happened 3-4 times in the three weeks I have had it. Ironically at the bank drive in all 3 times, which is about 1/2 mile from work, so I let the truck warm up for a minute or two, drive to the bank and sit in line and that's when it has done it. Not every trip, but each time has been after that scenario. I took it to a local garage and had the oil, filter, tranny fluid, and rear diff fluids changed and the chassis lubed. I told him of the issues and he said he would just plug it in and clear the codes, which he did. I specifically asked him to check the fuel system out. He told me when he was done that it was running lean because of the K&N style intake and wide open 4" exhaust, but he cleared the codes and it ran perfectly. Which was BS. The SES light came on as soon as I drove it out of the parking lot. After some poking around on this forum, I determined the lift pump to be the culprit. I ordered one from SSDiesel, along with a #9 PMD resistor (the PMD by the way is mounted with a "L" bracket to the side of the plastic 6.5 Turbo Power engine cover, which I know is not the preferred location. It had no resistor and is not mounted with a heatsink.) While I was replacing the lift pump and fuel filter yesterday, I left both batteries unplugged for over an our so the system would immediately recognize the new #9 PMD resistor. Truck drives great. No more stumbling, but the SES light still flips on and off under the same conditions as before. Sometimes I can slowly take it to 1,900-2,000RPM before the SES light comes on. Using paper clip and pedal method, I checked codes this morning and got DTC 36 flash around 20 times before I interrupted it and cleared codes. Since the truck would not perform over 70MPH until yesterday, I do not know if this next thing would have happened, but today I took it on the interstate and once I got to 74-75MPH, the SES light went OFF. Came back on under 71MPH. I have not checked the codes tonight since this morning's reset, so I don't know for sure, but I suspect I will see the same thing.

My question is this. The reasons I have found for DTC #36 is IP or PMD potential failure. Is one more likely than the other? Any other possibilities? Is there a way to test either one without buying one and "hoping" I got lucky and chose the right one? Any help would be great!

Thanks,
Ryan

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I just checked the codes this morning and I got 3 about 30 times an 36 about 30 times then interrupted the sequence with the pedal clear...