think the trans is shot

A little history on my boat: 1986 MC Tristar 220 w/ 677 hours on 351W. First trip out with new plugs and oil change. Running the best ever since i've had it. Put weight in it less than 10 times this year. Last year and the year before we had about 1000 lbs of sand in it. No problems.

Found a new cove to ride over the weekend. Drove to the new cove, pulled the girls. Two fairly short sets, no probs. Begin filling ballast...

Ballast full, my buddy hops in. Getting up on plane we hit something. Running gear not affected. We stop, check everything, trans fluid level, and start to tow again. At about 2000 RPMs its backfiring through the carb and just won't for crap.

In neutral, the engine runs fine. Feels like the trans is going... Maybe its old and not used to the weight...

Saw another thread where the guy was waiting for a trans rebuild and then realized the firing order was off. Not logical, but any chance its fuel/air related? All this began when we hit something...