8.8 swap

Detroit Locker 31 spline pn#71077
Yukon Gear Duragrip carrier pn# YDGF8.8-31-1
Either one, That should fix it.

Or rebuild the stocker with new motorsport clutches, with a new stiffer clutch pack S spring. Part Yukon Gear pn# YSPSPR-005
Friction modifier
Semi synthetic 75W140 gear oil as specified by Ford.