Chevrolet Repair: Chevy Tahoe Reduced Engine Power, chevy tahoe, chevy store

Question
What could be the issue?
I have an 03 Chevy Tahoe, 5.3L V8. I am getting the error P1516 Reduced Engine Power. I have taken it to several shops. Most recently they replaced a modulator that is located in front of the driver, bolted up against the frame closest to the driver. I never suspected this part, but he wanted to try it. I advised them to check the G103 Ground Wire as stated in the TSB for this issue. They said they bypassed that ground by grounding somewhere else, and that wasn't the issue. On diagnostic check he said the TPS and TAC were showing no discrepancies when he was able to duplicate the Reduced Engine Power. Now he wants to replace both sensors and the throttle body. I think this is a waste of time, but I don't have another solution. The problem only presents in the morning. After stopping and restarting 5 or 6 times it will let you drive it the rest of the day. I believe this is because the computer is set to test the data sets when the car goes from 40 degrees F to some magic number. I really am not mechanically skilled at all, but I know a little. Any advice is appreciated.

Answer
HI MATHEW, SORRY THIS TOOK SO LONG. I HAD PC PROBLEMS. I AM AWARE OF THIS TSB AS WELL. THE PO1516 CODE IS [COMMAND VS ACTUAL THROTTLE POSITION PERFORMANCE] WHAT WE HAVE FOUND ON MANY OF THESE FAULTS IS WHERE THE WIRE HARNESS IS NEAR THE THROTTLE BODY CONNECTOR HAVE BROKEN WIRES.. MOST OF THE TIME IT IS THE YELLOW WIRE. DON'T ASK ME WHY BUT IT IS..SO TO SUM THINGS UP I WOULD CK THE WIRE HARNESS TO THE THROTTLE BODY, WHERE THE HARNESS IS LOOMED TOGETHER AND PEEL BACK ALL THE HARNESS COVER AND CK EACH WIRE VERY CAREFUL BY EYE AND BY PULLING ON THEM AS WELL. IF YOU FIND A FAULT HERE GO THE YOUR CHEVY STORE AND BY A NEW CONNECTOR..WILL COST $75.00. THE FACT THAT GM STOCKS THESE THINGS YOU KNOW THERE IS A PROBLEM.. IF ALL LOOKS TO BE GOOD. THE NEXT STEP IS MORE THEN LIKELY TO REPLACE THE THROTTLE BODY..WE HAVE REPLACED THESE AS WELL,BUT MORE PROBLEMS ARE FOUND IN THE WIRING HARNESS.IF THE THROTTLE BODY IS BAD THIS WILL NEED TO BE RELEARNED [FLASHED]. LET ME KNOW HOW YOU MAKE OUT..GOOD LUCK,,,,TOM...