2003 GMC Envoy transmission

When started the car one day there was a lot of "rattling" noise coming from the engine. Tried to put it in reverse, but it wouldn't engage. Tried to put in drive and it engaged and the noise stopped. When driving, seems to switch gears only when letting go of the gas pedal and then giving it again, only then does the next gear engage. Basically, when rpm's reach a certain point, it starts to race without speeding up, unless you let go and give it gas again to engage next gear up. However, the reverse still doesn't engage. Also, maybe a month ago, the A/C only works when put on the highest speed.