Reply to "changing fifth gear to a taller ratio"

There are a variety of ratios available both for a change of ring & pinion and for changing only 5th gear. The stock ring/pinion was 4.22:1 and many if not all post-80s Panteras had a 3.77:1 ratio. A slightly modified Pantera engine can pull this taller gear with ease, and it gives better mileage and a more relaxed high speed cruise. Changing only 5th gear gives you the same cruise rpms but the stock lower R & P ratio still allows stock acceleration. Both methods are equally expensive and both require the entire transaxle to be disassembled, so now is the time to decide, since its presumably apart already.
FWIW, RBT Transmissions in the U.S long ago bought the world-wide rights to that model of ZF transaxle so all official parts- from gaskets to gears- will come from them. Others that sell such things are usually cannibalizing useable bits from broken ZFs, or they are not true factory parts. Caveat Emptor!