They do wreck the transmissions. Mainly because they are no stronger than the ones in the less powerful supercharged cars. Basically only the chain inside the transmission is upgraded over the V6 cars.
The V8's aluminum block transfers far more heat into the transmission than the V6's do and that will cause much higher transmission temps. High fluid temps burn out the fluid quicker and the clutches inside the transmission. A external cooler is basically a must if you live anywhere that gets luke warm during the summer times.
