1992 Chevy Cavalier engine running rough and stalling

I have a 1992 manual transmission chevy cavalier RS 2.2L I4. After driving for about 30 minutes on the highway the a/c starts blowing warm air and when I slow down for a stop light or stop sign the car will stall unless I turn off the a/c and rev the engine. There are times when it will stall anway after driving on the highway and then begin driving through town at slower speeds. It does start back up but the engine runs rough.

I have also noticed that my car is not driving as smoothly as it used to. When driving in 2nd or 3rd gear it is not a smooth ride but rather jumpy (like there is a pull from the engine) so I try and coast in neutral as much as possible. This will happen if the a/c is on or not.

I have religiously kept up on oil changes, tune ups, and filter changes. I also recently had all fluids exchanged (brake, transmission, coolant) and fuel injection cleaned. I also had the engine remounted and a new clutch kit put in. I just had the a/c checked and no problems with it. It works great and only starts blowing warm air after driving for long periods of time at 60 or 70mph. No engine codes when diagnostics run. What could be left to do? Could it be the timing chain? That has never been replaced and the car has 130,000 miles.

Thank you so much for your help.