I have a 01 Z71 with a 4.8. It has 127K on it. When I start it when the engines cold it will stay at around 1000 RPM's and then as I drive it, it will start to climb and will be anywhere from 1200 to 2K it will stay that way as long as I drive it and it doesn't make a differance how far I drive it. It's notthe throttle because I got out while it was at 2K RPM and the throttle was on the stop. Throttle plate looked all the way down. Now a couple of times at a red light I have turned the motor off waited like 30 seconds then restarted it and it ran fine after that. Got me a little confused . Anyway this is my first post and looks like a very informative site. thanks for any help. "J"

 

Its the Throttle position sensor on the side of the throttle body. When they go bad they do this.

Its an easy fix, just 2 t-25 torx screws and it comes out. though you do have to take the belt off, and swing the alternator out of the way to get at it.