99 suburban 454 p0123 code

My buddies suburban keeps throwing a p0123 code, when we clear it it immediatly comes back when the engine is started. we noticed if you move the tps wiring harnes the idle moves around, also since the check engine light has come on the transmission shifts late and hard. I know the p0123 code says "tps circuit high voltage" any ideas what can cause this? Does this mean the ECM is bad? What is it going to take to fix it? Any help is greatly appreciated.

Fixed it, replaced the tps switch no help. Turned out to be the wiring connector to the tps switch , spliced a replacement in and no more p0123 codes and transmission shifts correct.