It's not really a HP issue, but a torque issue. I think I read that our transmission can only handle up to 260 lbs/ft of torque and stock we have 230. Not much room for growth unless you take serious thought about the tranny.
That's another one of the reasons I'm going manual tranny. I'm assuming that the manual tranny from the Trooper will be a bit more robust as I'm assuming Isuzu accounted for the fact that it might be used for hauling.