Some gearboxes use normal gear
oil, some use an SAE30 motor
oil, and some even use ATF...
I used Redline Shockproof gearoil (lightweight) in the Torana's gearbox (Supra 5spd). The old Turdrunner completed hundreds of passes at the strip and a fair amount of street use using the Redline lubricant....
Redline Shockproof gearoil comes in heavy, lightweight and super light. I'd suggest the lightweight for the Tremec box.