My car overheats in warm weather IF I'm driving slow and/or without A/C on. on 2005 Chevrolet Malibu

I've had the thermostat changed and I think someone did something to the radiator or water pump a while ago, but so far, no fix has worked, or at least not for long. It only overheats in hot weather in stop and go driving or low speeds. If I put the A/C on, this fixes it. If I'm on the interstate going fast, the temp is generally stable, at least for shorter drives. I'm tired of paying people for fixes that don't fix the problem.

Asked by for the 2005 Chevrolet Malibu
your fan may not be working propperly, when you turn on th A/C the computer turns the fan on continuously,
when not running A/C it's controlled by a different circuit check all fan fuses and relays also have coolant temp sensor checked it maybe out of range...coolant level should be checked as well when engine is cold of course..
1 more answer , 2 more comments
See need to heat up vehicle and see if the cooling fan is operating.
Thanks SO MUCH! I will ask that someone check as you suggest. I figured that the fact that running the A/C prevents the overheating problem was a big clue to figure this out.
NO problem, post results so others may benefit..