I have a 92 SR5 V6 with the 5speed. I've been using the same Amsoil now for over 100K. The truck hardly goes out w/o a trailer most of the time. Still have the first clutch with 150K and I replaced the Amsoil with Amsoil again a year or so ago. I never had any problems. My detroit locker actually works better. I can always tell when the locker starts acting up that it's time to change the rear end. Also Amsoil. The older gear box might not be as sophisticated then the newer trucks but I thought they also have the R 150 tranny. Maybe with upgrades.