Hello all im new to the site and wish to ask for some advice the story is a bit lengthy but hopefully someone can help..

Well i have a 1991 rs camaro 5.0L 305hp automatic 4 speed 187+k miles and i had the oil and transmission fluid changed april and i was able to drive 1500 miles in long distance..

july 28th 2010 i was heading back to vegas from utah and all was fine but what i thought was broken tire was a solid object and since the car is really low it hit the middle of my car and completely messed up my automatic shifting it sent my rpms from 2200 to over 4000 almost red lining i had to pull over i couldnt put it in park ... park was drive 2 i believe so i checked no leaking or parts were loose checked the engine everything seemed fine but i couldnt go the normal speeed i would have to push the engine to 5000 rpms for it to shift so i can go at least 50-55 mph and then would over heat and would have to let it cool it took me 4 hrs to drive 100 miles or so.. please any advice or help to what could of happened

thank you