Is it a lock-up? I drive a 3400 stall 9" converter on the street (L/U) and you don't even know it's there... The TCC (clutch solenoid) went out once and my cruise RPM went from 2200 to 3100. That increase in RPM represents a bunch of internal fluid "thrashing". You shouldn't see any appreciable difference in heat if it's a L/U, but a non-locking converter will make a bunch more heat.