The transmission cooler should be near the radiator and fan. It's basically a small radiator. Be sure they didn't bang it and put a hole in it or mess up any of the lines connected to it while replacing the fans and sensor. And check for fluid leaks.

curious what sensor was replaced.... the fans wouldn't affect shifting. if there is a check engine light on have them pull the codes to see why its on... check the transmission fluid. sounds like it could be low. there is many sensors that could cause hard shifting so the check engine light code needs pulled to see whats wrong.

find local shop at ATRA.COM. the garage that did work probably doesn't know what to do next

Make sure it is full of transmission fluid and isn't leaking.

Give us some more information.

My daughter recently had work done on her 2005 Chevrolet cavalier. The cooling fans and a sensor had to be replaced. When she picked it up, the check engine light was on and it's shifting hard from 1st into 2nd. It was not doing this before it was worked on. It's now been back in the shop do a week and they can't tell me what's wrong. She's 17 and this is her first car and she has worked so hard for it. We don't have a lot of money and I'm afraid we are getting screwed. It's an automatic transmission.