2002 GMC Envoy with 159k. Starting it up has no problem and engine runs. Push on the gas and it revs up. Putting it in ANY gear and it just does not move. For a while there was a clicking noise under the vehicle, which i thought was the transmission. It started to die out on the freeway with a loss of power and I had to pull over and have it towed. That infamous clicking is now gone even though the envoy starts up. There was loud knocking coming from behind the dashboard after starting the engine. It would go on for 4-6 knocks and stop. While driving it I would start up the air conditioner and set it to "face" and not the feet or combined setting, I would hear that loud knocking again. I have gotten all kinds of feedback from people, just replace the whole transmission and so forth. need some advice.