I would go back to a 180* thermostat just to allow the coolant to begin circulating and disappating heat sooner... Also, are you running a shroud ... If not, it would help because it focuses the air flow through radiator better. The number of cores on your radiator may be a problem because of less cooling surface on smaller radiators. Also, check your timing.. If you timing is somewhat retarded, it can make the car run hotter... BTW, do you have a fast idle solenoid to bump the idle when AC is on ?