what grade of Royal Purple do I put in gear box?

 

You want a 75w90 GL4 oil. Not sure if RP makes a compatible oil or not. Frankly, I'd pony up for either the Amsoil or Castrol Syntorque. Rebuilding a nv4500 is more expensive than the correct oil.

 

Funny you say that, cause I'm having mine rebuilt now cause I didn't put recommended fluid in it. Only took maybe 10-12000 miles to kill it.
My tranny was clicking and knocking in 1st, 2nd, 3rd and 5th gear. Sounded pretty bad and my mechanic told me it had teeth missing off gears, syncros were toasted. oh wells.

But I like to look at the bright side of things, my truck gets a rebuilt tranny!!

Final word: Make sure you put up the $$$$ and get the right lube.

 

i used amsoil in my last truck and it worked great. and its alot cheaper than the castrol stuff.