While it's true you can get a tuner to push the hspwr on your engine, your also pushing the limits your engine is warranted for. You break it your going to pay the repair bill. I've heard on many sites guys pushing their Cummins power and blowing heads and gaskets and pistons,etc. Not to mention the other parts of the drive train. Transmissions can get real expensive.
Pick the right MH with the right engine and you won't need to worry about it.if your the type that needs to get to the top of the hill the fastest then make sure you have the correct engine to do it. It might get you there the faster adding a tuner, but it could cost you lots of cash in the long run.