2005 GMC Envoy No gears

Is the transmission fluid clean and full? Is the check engine light on?

Fluid was normal and no lights at all came on. We changed fluid and filter just in case but still nothing

Without a light, it becomes a guessing game. If I had this in my shop, I would first start by checking fluid pressure. There is a pressure switch that can go bad, a pump, and the torque converter.

Can you tell me how i would check the presser and the presser switch or the tork converter

Basically, one uses an oil pressure gauge and splices it into one of the transmission cooling lines. That will identify what pressure is present. Once that is done, then it becomes a process of elimination... checking each component to see which has failed.