Re: T4,What kind of lube?
Sorry I have to disagree with the other post. The T4 and T5 transmission use automatic transmission fluid. Since you have put gear oil into the tranny is it harder to shift into reverse; does it grind more if you don't shift into another gear first? The reverse gear is a free spinning gear and the thicker the oil the more it spins and the more it grinds.
You probably will be ok with the gear oil, but the factory recommendation is dextron. Why don't you just call a Jeep dealer and ask them instead of a third party manual or a parts store.
My CJ had a T5, now upgraded to a World Class T5, and the factory recommended lubricant was dextron. As far as I know the T5 is a T4 with overdrive.
Just my two cents.