Hello, my 91 RS runs perfect when I start it up and drive around, but after say 10-20 miles it looses a bunch of hp. After start up, when the car switches gears while driving, it smoothly switches gears(with only a slight kick), but after driving around the gears switch horribly, like I feel the car fall back and weakly come up in gear. When this is happening, if I hit the gas, I can hear a knock like almost on top of the engine, but it doesn't knock in park or neutral.

The knock is like a metal piece hitting something over and over, faster with higher rpm, It sounds belt related though.

Any suggestions? Sorry if I didn't explain this too well.

 

Sounds like you may need to look for a new/rebuilt short block.

 

I mean it sounds like something to do wit the belt, but as i said, car runs amazing when its not heated up, also my oil pressure stays right above red at idle in drive.