like spyder said what do u have in mind????? the most common are a new traction lok, or eaton, some moser axles, 4.10s and all new bearings and seals. if u are going to do some serious drag racing some 35 spline axles 4.88 gears and a spool ;D ;D
for me if im gonna turbo/supercharge mine i'm going with 31 spline's and a 31 spline carrier. those carriers are usually cheap and found in alot of ford trucks...i do that if i was changing gears. i wouldn't though just to beef it up...moser 28 splines or strange can handle a pretty good beating.