CM871 poor power and fuel econ

[Grounded Pilot]

Rebuilding this motor is probably in the not so distant future, but my pressing issue at the moment is figuring out why it’s throwing a 974 cab side code “tps low voltage” (according to the mechanic/insite). Just replaced the sensor again. All three sensors (I still have all 3) read the same voltage outputs at the sensor and at the inputs to the ecm. With a constant 5v supply to both APS and IVS circuits under all conditions, so I’m assuming it’s not a sensor problem. Motor running or not, throttle pedal depressed or not. But the thing throws the 974 code constantly. Idling in the shop or on the road. I have cleaned and polished every connector on the firewall multiple times and flushed with methanol. Just figured out that this thing had a pto and it’s been removed. Is there a secondary computer somewhere I should be checking for a aux throttle input??? Or any other ECM reasons that it would be throwing that code??