I have a 2003 Chevorlet Trailblazer LS 4x4 with a straight 6cy motor. It runs fine except the fan runs sometimes. You can start it right up in the morning and the fan will run and it will sound like a jet plane taking off while your driving, then other times the fan wont come on. We just got the car and they said they changed out the fan clutch and the temp sensor, but idk why it does this. When the fan isnt running the car runs fine and RPMs stay low, but when it is on the RPMs run high. What could be causing this?