1992 Toyota Camry

Transmission problem
1992 Toyota Camry 6 cyl Front Wheel Drive 147000 miles

i have a 1992 camry that I recently purchased and it has a new radiator and supposively a new transmission. What the problem is that I am having is that when the car is already warm, when I put it into gear the rpm gauge goes up to 2000 then back to 1000 then 800. And this seems to happen also when I am coming to a stop, it seems to be reving to high when it shouldn't be. Also the fan runs continously. The garage told me it might be a sensor from when the new rad was installed. That might not be plugged in or not working or a broken wire. Is this a shot in the dark for them or is this possible. And would like to know where these sensors are so maybe I can find the problem myself.