syn. fluids

[KPittman]

Gentlemen, I'd like some advice on syn. fluids. Is Tgr series 2000, 75w 90 a good or possible the best syn. to put in my 5 spd. and differential? I was told that by the company, and would like some input. My dually is a '95 with 252,000 stock. Only had it about a year. I tow a 7800 lb. 5th wheel camper with it. Rear end ratio is 3:54. Thanks much Kirk Pittman