Yes Gl-5 is fine for rear diff and t-case AFAIK. My 1Gen tranny didn't shift nicely with the royal purple seemed to thin causing shifter block @ higher revs. The 1Gen tranny is much more sensitive to fluids as the syncro's where not a perfected design, the earlier the tranny the worse the syncro & hub assembly engagment became, and they changed/revised the design every year from 89-95, not sure bout the later.