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 ????