just a thought. Try and adjust the pressure plate to disengage the clutch discs more. The maybe still grabbing enough to keep the input spinning. You need at least .060 or so to keep things happy, use a feeler gauge between the disc or in your case discs to see how much clearence you have. But as others have said that OD is on borrowed time.

With 29" tires 4:10s and the 18-spline 55mph should be around 3300RPM.... Put the 3:54s in it that thing has a TON of torque!!!!! You wont need the OD then... Good luck

I want to add also make absolutely sure the gear oil in the trans is GL-4 rated not the newer GL-5 Stuff!!!! Gl-5 rated has too many friction modifiers in it and it doesnt let the synrco grab the gear effectively causing lazy shifts and grinding. ATF may work for you too as others have used it but I am sticking with my guns of GL-4 rated 80-90wt. It may be tougher to find the Gl-4 stuff but it is out there still...