Guess I should have asked the towing guys here first, I want to be able to easily pull 20-23k, with the dually, at first I was thinking around 400hp, is this high/low/correct, I don't want to over do and lose longivity, this truck is a keeper, thanks.

Depends on how you build it. If you don't cheap out on quality parts, and make sure you keep enough air for the fuel you have to keep things cool, you should be fine. Make sure you get gauges so you know when to back out of the throttle.