For future readers looking for a possible solution.
As mentioned by GMMerlin, thanks, cleaning the throttle body solved the problem.
I have a 2000 Tahoe(new body style). The throttle is electronic no cables. There is no IAC (idle air control) that I could see. So, my conclusion.. since the throttle is electronic it can be control by the PCM and simulates the IAC to maintain a set idle. The build-up on the the throttle body confuses the PCM causing an erratic idle and stalling. After cleaning the throttle body the idle was solid no irratic idle.