To check the clutch, , engage the hand brake, slowly let out the clutch, if the motor dogs out and acts like it wants to die, your clutch aint too bad(Not a test you want to do too often). If the rings are bad, compression/leak down test will diagnose. Sounds like some thing with the AC, more so than the motor to me. Could be the ignition timing messed up too, which can make you run hot. Does it run hot with the AC off?