Overheating 94 Tbird

My 94 tbird has an overheating problem. I have had the thermostat, water pump, radiator rodded, cooling fan replaced. It will overheat even on the highway (75mph). If the outside temp is 90-100 I have to constantly watch the temp gauge. You can watch it creep up towards the red line on the gauge. If I climb up any kind of hill you can watch it go up. I have to shut off the a/c just to make sure it doesn't overheat. On the same trip if I go down the other side of a hill you can see the temp gauge drop to what would be considered below normal temp. Every other aspect of this engine is great. I have 250K+ miles on it but the engine runs great. I get 25-26 mpg consistantly (same as when it was new). There is no smoke, white or otherwise. The air deflector under the front end is no longer there. Could this be part of the problem? Any suggestions?:runaround:

If you replaced all those parts either you have vapor lock, blown headgasket, or you despertaly need an oil change.

Thanks for your response..................I don't see it being the head gasket (no smoke & great gas mileage) and the oil is changed every 4M since it was new.