I'm assuming you're still using the 14mm? You really should move up to some 17mm or 23mm wheels. Moving to metal hexes will help for a while,as mentioned above,they need to be on tight.
I'd say go with some stock size tires, steel hexes and back off the slipper. Too tight of a slipper adjustment will just send the shock into the diffs with the steel hexes. Slipper adjustment is critical, even with a beefy drive train.
take the hex and jb-weld it to the wheel. then take two pins used for the axle to hex and drill a hole for it parallel to the axle through the hex and the wheel, then the pin goes through the hex and the wheel. this might work.
I have not looked at the size but they are about a 1/2 inch taller than the stock ones, but i think the jb weld and a pin trick might work, slipper is set farly lite the guy built it for jumping. Thanks guys