[fastlane]

Stock units are good for about 500tq because the torque convertor will multiply torque at the input shaft. If you are making 450-500tq at the engine, the input shaft will see almost 1000ft.

I am running a 4R75W in my car. I am making over 900hp/800tq at the tires. Knowing I was going to push the limits of the trans, I had it built before installing. Speaking with my builder, the biggest issues are the stock clutches, input shaft, convertor, line pressure, and sun gear shell. There also needs to be some additional oil cooling of the tail shaft. When my was built, we installed Alto Red Eagle clutches, billet input shaft and sun gear cage, upgraded bearings, and an external line to feed trans fluid to the tail shaft. If you want the clutches to hold, you need to bump up the pressure in the valve body. You can do things like the JMOD or install a shift kit to help. I went the route of having my builder rework the stock valve body to his specs in order to achieve the proper line pressures. Bumping the pressure can cause the stock convertor to balloon so I highly suggest getting a good aftermarket convertor or have one built to your spec. Mine was a custom built unit and I couldn't be happier.

Don't forget to install a good transmission cooler just to keeps things cool. Heat will kill the clutches and never do a WOT 3-4 shift at higher power levels, you will grenade even a built trans if you do.