'01 Venture Transmission Problems
 

A couple days ago, I went to back up out of the driveway and it was like a ran over a bike or something...I put the van back in drive and then park and went out to look and there was nothing there. The transmission just slipped like as if I was running over something, but then it was fine. It was fine all the next day. Then went to back out of the driveway again and no reverse. Went back to park and drive and neutral, and back to reverse, thinking it was maybe just slipping again, but nothing. When in neutral, it wants to go foreward....put it in drive, and it will go in D, but it is sluggish and revving higher than it should. Whats going on???? It has about 250,000 km on it. Had the transmission flushed about a yr ago. Fluid levels are full now. Any help would be great.