In the NV4500 its recommended to use ONLY CASTRO SYNTORQ.

I have heard to make shifts easier especially in cold and better compatibility with the synchros. Anyone switched to amsoil or other synthetic gear oil?

I have had good luck with redline synthetic in my tranny and some others also. I have also tried mobil 1, but it seemed to get dirty faily fast. If you want to run syntorque, do a search for Standard Transmission in Texas, they sell 1 gallon of syntorque for about 45.00.

Standardtransmssion.com does have the syntorq for $54/gal +shipping.

http://www.quad4x4.com/index.html also has it for $25 for 2 quart container.

They too look like a good source for NV4500 parts ect.

I have read some more on the internet various places and am a little scared to change from the Syntorq.

For what its worth:
One of the more reasonable stories I read was Castrol made an agreement with GM and DiamlerChrysler not to sell small containers of Syntorq. Places like the above are buying it in bulk and repackaging it. This makes me nervous.

The local Chevrolet dealership had no clue about Syntorq (no surprise). It appears they bottle it with GM or Mopar part numbers only anymore.

For the NV 4500 you can use Amsoil severe gear 75-90---check it out on the Amsoil corperate site!! This oil will out perform!! It will shift better--take heat out!!

Greg Carter Vermont

Amsoil has a new product that should be out any day now just for these trans. Price will be way cheaper than Syntorq.

Greg