5v reference issues

I have a 2007 GMC Yukon XL Denali with a 6.2l. I all the sudden got the reduced engine power that disabled my throttle. I drove it to work and got in to leave and it immediately popped the code P0641(5v reference circuit 1). I am at a loss for where to go now, I have 5.05v at my sensors, cleaned all the grounds, unplugged all the sensors and spent 2 days going through the entire harness. I borrowed a snap on solus edge from my old boss and started going through the data, the ECM says it only has 2.83v but if I back probe the map sensor I am still getting the 5.05v. I am thinking it's a bad ECM...... looking for confirmation or other things to check.   

I also want to add that your videos on the subject were very helpful with checking problem areas first, thank you for posting them!

What voltage are you seeing at the ECM? Not scan data, but AT the computer.

I have 5.05v back probing the wires at the ecm

Sounds like the computer isn't very smart any more.
The rest of the sensors on 5v 1 circuit are: APP2, AC pressure, brake booster, cam sensor, oil pressure, fuel tank pressure, and as you know MAP.
I don't think you need to check them all for 5v, but I would just for the sake of being thorough before selling a PCM along with checking powers and grounds at the PCM naturally. But I think you're correct and that it's going to need a PCM.

I'm curious if you can read voltage on the ECM case.

No, the case has .3 MV, and checking the ground wire it also has .3Mv.

The only sensor I have not been able to verify at the sensor plug is the fuel tank pressure sensor, I have about 22gal of fuel in my tank right now. I did check the wires at the computer....5.05v, 1.43v(signal=ok to the baro), .33MV on the low reference (matches the main ground on the computer). Next question would be stick to OEM and tow it to the dealership or buy one online with security disabled? It does have 252,000 on the clock so I am only looking for a few more years.

I would put a used one in. That generation should only need three ten minute key cycles to learn the anti theft