I'm still using regular off the shelf gear oil, however mixed with Evo9 MR Diaqueen, in a 2:1 or 3:1 ratio. Transfer case uses straight regular off the shelf gear oil and so does the rear diff.

My car is making 830WHP/650 ft lbs ,3300 lbs with me in it, running 10.0's and 149 MPH in the 1/4 on a stock syncro transmission, stock transfer case and stock rear diff, and it's still working for me.... I recommend the same mix to all my customers with high power level and it works for them too...

These transmissions were designed in the 90's and used regular gear oil back then which worked well for longevity and durability. Along came the fancy synthetic fluids which IMHO just accelerate bearing, syncro and gear wear for a quicker shift. With the transmission I build these days with double syncros, new hub/sliders and proper clutch adjustment, fancy gear oil is simply not needed in order for it to shift nice at high rpm.

People still ask me over and over again what I'm using in the transmission to keep it together. I keep telling everyone the same thing: regular gear oil will make the transmission last the longest