Guessing your PTO shaft is too long. At some point between lifted up, and working position, guessing mid-range the PTO shaft is collapsed as much as it can and all that thrust has to go somewhere. Most manuals that come with a PTO driven attachment states to check that. If too long, cut both end of the shaft a bit to match your tractor so it won't do that. You'll have to remove the shaft guard to do that. Probably didn't do the PTO shaft bearing(s) any good either.
To repair the A-frame, remove it and lay on a good solid surface, and work on it with an 8-10 lb. sledge to straighten it. Same with the ears on the tiller it bolts to. If it bent cold, straighten it cold. As far as the yoke, run it until it has pups. From the looks of the tines, and you bought it new, it's been doing that from day one.