I'd install a center diff if you can find one that fits. That would eliminate all the rotational mass of the transmission.
If you can't find one that will go, I'd suggest an RRP idler gear for the tranny, and install a forward only conversion if you havent already.
You'd also probably need things to make the truck pretty heavy. Aluminum wheels, heavy things to make it more massive so that it would pull better instead of spinning tires.
Also, gear it as low as possible. 12t clutch bell, and as large as a spur gear as you can find.
Hope this helps.