Fault codes
 

I'm getting a check engine light and the truck goes into limp-home mode. The codes are P1516,P1517, and P1518. I changed the throttle position sensor earlier this year because it would shift out of first at WOT. Should I change out the TAC module? It's a 03 6.0 out of a Yukon Denali. Thanks for any help.

Re: Fault codes
 

Did it ever function normally, or did it start throwing fault codes pretty much right away? Were these parts all from the same donor?

Those codes are generally something you'll see when there is an equipment mismatch, but if they functioned together before, then we need to look at individual components.

The yellow and purple wires on the throttle body are notorious for pulling out of the connector or breaking within a few inches. Check the ground wire from the TAC, and try isolating it from other grounds.

Re: Fault codes
 

Yes I did the swap a couple years ago without trouble until this year. Changing the position sensor made the shifting a lot better and that was a couple hundred miles since I changed that out. I have checked the yellow wire to the servo. I gave the wire and the connector a good tug to see of it was loose or broken. I have the TAC module bolted to the inner fender well.