2003 L200 Hard Shifting

My 2003 L200 has 99,000 miles on it. The car runs smoothly for about 10 minutes or so - until the engine is no longer cold - then something weird happens.

BOTH radiator fans begin to run. I don't think I've ever heard them both run. And, as long as they are both on, the car shifts extremely hard. Like with a big boom. It slams into drive and reverse, and slams into every other gear when shifting.

The check engine light has been going on and off periodically for months now, so I had that checked out. The only signal was for a bad idle temp sensor. I replaced that. When hooked up to diagnostic equipment, the computer still reads -40degrees (f) which indicates that there is still no signal from the idle temp sensor.

I'm afraid to drive the car this way, because I don't want the transmission to get damaged.

Can anyone explain to me what’s going on?

I have asked 4 mechanics and none of them really had any definite idea what the problem might be.
please help!!

thanks

a bad temp sensor can both turn the fans on and cause abnormal shifting.have the codes checked again(autozone does it for free) to besure. if the correct sensor was changed(as there are several temp sensors that do different things) then it may be a bad connectior or wiring problem