400WHP on pump gas? Get a FP Green or some sort of 50 Trim, you'll love it.
Hey, is the 347WHP with a stock turbo? If so do have a FMIC? If not look into one just to get rid of the top mount, I never liked them, why put an aluminum cooling piece DIRECTLY over an engine? I know its great for throttle response, but as long as you get good hard piping its just as good if not better with tuning.
FMIC would cure MANY Detonation issues, larger more efficient core and survface area. Do you have stock injectors? Or do you have aftermarket?