Originally Posted by Wattles

Twin turbo on an auto can put a lot of strain on the auto that is built to handle only 330 - 350hp. You can easily get 600+ hp with a good TT setup and that will strain the stock tranny pretty good. This can lead to failure and/or costly repairs.
Many people choose to go with aftermarket trannys or upgrading the stock ones with new internals or valve body upgrade/line pressure increase to limit slippage thus reducing heat & wear. A transmission cooler can also help to keep wear down.
A major issue for auto transmissions versus manual is that virtually all of your shift will be at or near maximum torque and maximum turbo boost. This is in stark contrast to a manual transmission where you engage the clutch and lose boost pressure while shifting then build it again after the next gear has fully engaged. (Unless you are power shifting)
This reason alone causes massive stress on an auto transmission that is not a matter with manuals.



I have experience with my AT that even with a valve body upgrade I am still seeing some slippage in higher gear changes (4th and higher) but it performs very nicely with over 500whp on my IPL. The main question for me is how long will my trans last...
Good luck!