Transmission problem
2004 Buick Rendezvous 6 cyl Two Wheel Drive Automatic 48000 miles
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It was driving just fine then all of the sudden it wouldnt move. The RPM's were going up but the spedomitor wasn't moving. I shut the car off and turned it back on and it started moving again and then it did the same thing about 200yds down the road? I've checked all the fluids. what could this be?

It could be low line pressure in the trans, or a damaged seal that is causing loss of pressure to a clutch pack. It sounds like it needs to go to a tranny shop.