1998 Chevrolet Venture • 6 cylinder 2WD Automatic • 220,000 miles

My 1998 chevy Venture transmission wont go right into gear when I start my van up, it has to be reved up for about a minute then it will go into gear, it also seems to go into neutral after driving for about 10-20 minutes above 50 MPH, then I have to sit on the side of the road for a few minutes then it will be in gear again once I start the van again? Also wondering what vehicles are compatible with mine to get a used tranny from if needed?
May 31, 2011.

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