Put my tranny and transfer back together and I put Valvoline Synpower 75W90 gear oil in it. A friend told me it says on the side of his that I should use Castrol Syntorq GL4. What's the difference? I know the Valvoline is a GL5. Is this a big deal?
My tranny is very hard to shift when truck is running. We rebuilt the tranny and transfer case so a bunch of possibilities exist. Clutch doesn't seem to disengage completely thus not allowing shift into gear. Only 70 miles on it since rebuild and it does seem to be getting better. The warmer it gets the harder it gets.
Could the gear oil be the problem?

Well, the NV4500 should have Synchromesh in it. As far as the difference between the valvoline gear oil and the synchromesh? I would imagine there are a few additives that are a bit different. Dunno how much difference it's going to make though. :confused:

To be on the safe side, I would probably put it what it calls for...That might be part of your hard shifting problem too.

When I done my nv4500 swap I too looked around for another choice of oil wound up not getting a good answer from anyone. Went back to the dealer and bought what the tranny called for. Advance auto has a pensoil syn. lube now that is supposed to be rated for a replacement of the syntorque or mesh oil in this tranny.

Sounds like air in the line, bleed the slave when it's hot.

I geuss why take the chance over 40 or 50 $. I'll get some of the oem stuff or equivalent from the dealer or advance and change it. I'll try the slave again too. Tranny does good when it's cold but gets harder as you drive. Hope I've not damaged anything in 70 miles.