Most GM vehicles with a modern TAC control have an APP assembly has 6 wires and each individual APP sensor has a 5V ref, low ref and a signal wire.
This is the schematic for the 2008 Tahoe TAC and APP circuits.
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So if you have high resistance on one of the low ref circuits, your 1-2 correlation will be off. Or high resistance on any of the individual circuits.
That being said, loose terminals causing the 1-2 correlation in the APP or the TP sensor circuits is so common GM released a PI for this concern, PIP3783D.
If you replace loose terminals, do not use crimp style butt connectors to fix, the problem will come back. Solder in connections have the least resistance and will fix it permanently.
Not saying this is your problem but it would be worth a look!