Intermittent reduced engine power

[Giblu427]

Working on my uncles work truck, he has a 2004 GMC Sierra 2500hd 4wd  with the 8.1l vortec.His problem is it intermittently goes into reduced engine power. There’s no rhyme or reason for it, I could drive 200 miles no problem or back out of the driveway and go into REP mode. Hot, cold, rain, sun doesnt seem to make a difference. The hard set codes were p120, p220, p1516, and p2135.  It has a new throttle body assembly, tps connector and  harness , pedal assembly, tac module was swapped with a junkyard unit but made no difference so he threw the original one back on. He did the “throttle relearn procedure”. I say it that way because I’ve seen several different ones, he did the “idle 6 minutes, key off 60 seconds, rinse and repeat”. So what i’ve done so far is check current on all grounds. Found and replaced a burned up ground wire in the pedal harness (app3 low reference) checked,clean, and tightened all the grounds on the engine block and frame, all grounds are showing good current flow, continuity, 0 voltage drop and less than 1ohm resistance. The 5v references show a slight voltage drop of about 100 millivolts each, good continuity, less than 1 ohm of resistance. Same with the signal wires. However, the 5v reference wire and signal wire for tp2 is showing some weird stuff. With everything connected as normal and the key on engine off, tp2 signal is at 0.78v and the 5v reference is at 4.26v. With the harness disconnected from the throttle body and the key on 5v is showing 4.99v and the signal is at 4.91v, if I plug in the connector with the key still on it changes to 4.88v(5v reference) and 1.12v(signal). When I cycle the key off and back on with everything connected it goes back to the original readings (4.2v at reference, 0.78v signal). Tp1 connected and key on shows 4.88v(reference) and 1.14v(signal). Just out of curiosity i also jumped the connections for tp2 alone to the throttle body and it read 4.88v at reference and 1.12v signal. Did it with tp1 and showed 4.88v reference and 1.14v signal. I jumped them at the front of the connector and in the back with t-pins and got the same reading either way. Also I had the old throttle body laying around and plugged the harness in there and got the exact same readings. Also the battery is reading 12.2v and im sure it wouldnt hurt to charge it. I ordered a scan tool that can do throttle resets but until then what would my next step be here? I have wiring diagram attached, the blue/black is tp2 5v reference and purple is the signal