Hay guy, I just got my wife an 02 Tahoe 4.8 LS 4x4. Runs fine but in the heat of the day in Tx 98 + deg only when the ac is on, it overheats! I have replaced the thermostat and fan clutch, there is no leaks or loss of fluid. Radiator looks clean thru fins. I can turn off a.c. and turn heat on and the gauge will drop almost instantly. Can somebody please drop some knowledge on me for this one?