I thought they were kinda slow stock. They dyno in the low 400s at the wheels stock, but they have to wiegh around 4000lbs. They feel like a tank.
They like mods though, intake, pulley and a tune is good for around 500whp. Add header back exhaust and it will be close to 550whp. Here is a video of one we did this spring
http://www.youtube.com/watch?v=ZBjDXEPIZYI It put down 413whp stock. It still has stock motor, stock clutch, 100% stock fuel system.