One should also note that "regular" automatic transmissions also have a maximum torque handling capability. If you put twice stock power output through a standard automatic, it will definitely fail. Some automatics start slipping after you've only added seventy to a hundred horses more.

The tuner's job is to give the client what he wants. If he wants more power, damn the transmission... that's what he gets. But in any turbo tuning or install, new clutches, or, with a torque converter automatic, an upgraded torque converter and clutch packs, are a very, very good idea.