Automatic Transmission problems of the 2000 Jeep Laredo

I have a 2000 grand cherokee. With 4. 0l, auto trans. , 4x4 select trac. It shifts hard taking off from a start. Seems like it double shifts while increasing speed, goes from 2nd gear to hiigh gear then back to 2nd gear and then back again all within a few seconds. I took it to a transmission shop where they explained to me about the possibility of an o-ring seal that was to small and to replace it would require the transmission to be removed from the vehicle. Very expensive. I haven't had the repair completed yet. Before I take it in for repair, has anyone else experience this problem and or another fix?.

Another vehicle and mine was backing out of a parking lot and backed in to each other, no damage done, I parked my truck, got out and the vehicle went backwards and backed into the same vehicle again and did damage this time.