Thanks R. Pope, that was my guess too. What is the present rear gear ratio? lt seems to me it would be a lot easier to lower the rear ratio by a tooth or two than to change the trans and lose the OD. As far as the slippage goes that may be a mismatch with your stall rpm and the low rpm in OD. If the rear gear were lower you might get above the stall rpm and that would cure the slippage?

Don Shillady
Retired Scientist/teen rodder