I use amsoil for everything. Tcase, trans, rear diff, and motor oil. Been using it for 3 years with no issues. This is on a heavily autocrossed/tracked car with a decent amount of power.

75w140 Severe Gear for the front and rear diff (both aftermarket)
75w90 Manual Transmission fluid for the trans
15w50 Dominator Racing oil for the motor

 

Use oem oil

 

Reviving this thread in teh hopes that some of the bigger power guys (600 whp+) or dedicated racers get on here.
I just had my bone stock transmission torn down and found that the OEM fluid did not hold up to 650whp. Issue I'm running into is all five gears getting heated and on the verge of catastrophic failure. I'm rebuilding my transmission with revised gear ratios and upping the power, but am a little concerned about having another failure.

I'm hearing that a heavier gear oil is being used successfully, but under what conditions?