I used Valvoline SynPower in both the front and rear diffs on mine. I just used the same weight in both 75w90 is fine to use in both of them. It also has LSD additives in it so you dont have to mix if you have LSD. If you dont it wont hurt anything.

--Dave

1999 Rodeo LS 3.2 4x4 5 Speed
32x11.50-15 BFG T/A KO on US Wheel 94 series
3" Lift - Rancho 9000x
Rear No-Slip Locker
Flowmaster 50 series SUV 2.25"

There is a very fine line between "hobby" and "mental illness." - Dave Barry