COLANT TEMP SENSOR

I own a 2000 Ford Taurs SE V-6 3.0 L OHV, 197,000 miles on it. Back in March I had the Coolant Temp sensor replaced allong with the EGR pressure Sensor. Since these 2 sensors were replaced whenever I turn on my heat or A/C the rpms conisistently jump up and down on the engine. I don't mean the occasional jump when the condensor or fan are pulling more from the engine, it's a constant non stop jumping and it jumps almost 1k. The car did not do this prior to these two sensors being replaced. I'm in Denver, and this week it got hotter then normal, up to 102. I was driving in the heat of the day, did NOT have the a/c on, just the car running and the radio running. My car temp gauge went up to the hot mark, and starting running rough, like it was trying to stall. I parked the car checked under the hood there was no steam, no hissing, no broken hoses, no leaks, etc. The coolant system was just flushed 9 months ago. Any idea what this may be? When I called the shop who did the work the first time I was told I was crazy and cars rpms jump like that normally (I know they don't). And now I'm told a coolant temp sensor has nothing to do with this problem, all it does is tell the computer to tell the engine when to run the fan, open the thermostat etc. Well then it seems to me that that would be the problem. Thank you for any help or advice you can provide me. I feel like this shop is trying to rip me because I'm a woman.