You may want to pm chris kemp - DOHCZ34 for a tune, quality stuff and is pretty seasoned with all sorts of 3800 setups. - View Profile: DOHCZ34 - Pontiac Grand Prix Forums : Grandprix
I would also be worried about belt slip on the 3.0 with that belt setup. Something like this may help - Belt Wrap Kit
With those mods and the way you are going to be running it, you're going to need some 42.5# injectors as well.