1996 Dodge Caravan shifting problem

What I would try that has worked for me on a Dodge Caravan that started doing this around 160k miles and has done it every 20-30k miles since is to purchase some throttle body cleaner in a spray can. Remove the air intake at the throttle body (hose clamp needs to be loosened to remove. Hold open the butterfly that the throttle cable is attached to by rotating with your hand and spray until the residue running out is no longer brown. This fixes my shfting into high problem. The other thing it fixes is stalling at traffic light idle that happens around the same time.