NO, no, and NO. Syncromesh fluid is for the light duty 5 speed. (Getrag, HM290, 5LM60, NV3500 - all those variants)
The NV4500 requires Castrol Syntorq LT but you generally will not find it packaged as such. It was developed by Castrol for use in the NV4500 - mainly to protect the carbon fiber blocking rings (synchronizers) used in this transmission. You will find the fluid sold at GM and Dodge dealers. GM's part # for it is 12346190 and it's called simply "Synthetic transmission lubricant" or something like that. You need 4 quarts. It's around $20/quart.
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You can believe other people that tell you they used somethingorother fluid this or that, but they won't be the ones shelling out $1K to rebuild YOUR transmission, rite?
Richard