Well I would be looking hard to the converter. Reaction times obvious would change with tire slippage, but if it is dead hooking and running slow on the tree and 60' I would be looking for a converter to toss in it for sure. Might look at the trans as well but sure sounds like a converter issue to me. Just went through this on a biddies S/ST car. Pulled converter and found some fins had been knocked loose from brazing, same deal. Reaction times and 60's inconsistent down track was fine.