Idle problem

I have a 2002 Yukon 2wd 5.3 lt engine. This vehicle vibrates while is in drive and completely stopped (i.e in a red light). I did the complete tune up, change the PCV valve, wash the throdle body, computer diagnostic and everything seems to be ok. Does anybody know how to solve this problem??

I took it to the dealership and they said that probably is an exhaust problem.

Thank you.