in the differentials you can use 75w-90 or 75w-140 and if its posi you need additives, the trans and transfercase use just normal ATF and i believe 96's used dex 4 (you can use AMSOIL universal ATF and not worry about it because it covers most automatic transmissions out there) and you dont need additives for them, if he has the owners manual have him look in there because it will tell him the correct lubricants to use,