I have a 04 TJ with a nv3550 . Besides factory whats the best fluid to run. And should I stay with the automatic tranny fluid in the transfer case it's always worked before. Tranny has 9k on it and is starting to grind here and there . I have heard everything from Mobil 1 10-30 with a little auto fluid to amsoil and CASTROL SYNTORQ LT . Anything I'm missing .

If you don't use the right oil it will eat the synco's. Penzoil has a oil designed for the NV3550. It is Pennzoil Synchromesh. Here is a link:

http://www.pennzoil.com/products/gear_oil/syncro_fluid.html

Good luck.

Thanks , anyone else ?

http://www.syntheticoilnlubes.com/amsoil_5w-30_manual_transmission_fluid.html