I recently purchased a 2006 GMC envoy Denali with a 5.3 engine. I am having a problem with the engine stumbling, hesitating, and sometimes backfiring. This problem seems to occur when I decelerate and step on the gas to go again. This does not happen all the time. I have taken it to GM and they still cannot find a problem. So far the following parts have been installed new catalytic converter, mass air flow sensor, cam sensor, crank sensor, change the air filter, cleaning throttle body and flashed PCM. This problem always occurs when I decelerate and then accelerate again. When the problem occurs it does not store any codes. Any help would be greatly appreciated and this is a great site thanks you
