Thoughts are this... Put the 3.8 back on till tuned. If you're gonna play around with it, continue modding, etc., then HPT is a worthy investment cause the boxed tune is half way there ($).
HPT site, here and many other resources to get you going with tuning. You should start with a base file anyway and then a weekend (for noobie) of driving and adjusting will get ya your own tune. Starting stock and working down to what pulley you want, always adjusting for the ever engine killing knock. With a boxed tune you may still have knock, then what?
Only and best way to go is in car tune.
my $.02
