I'm guessing you have cut the airbox top or otherwise modded it to flow more air? If not do it. Then you have a few options...listed from cheapest to most expensive:
1 goto the stealership and get the trimmer bumped up a bit to even out the a/f ratio...$10 I would guess
2 Get the PCIII, install a map on the PC based on you mods so far.(no dyno needed unless you feel like throwing cash around)...
3 Get the FIM U5.9 thingy which should come with the correct map, if not get the correct map for your mods.

You could also purchase a MDST from chris over at ca cycleworks and bump the trimmer up yourself. ($249) If you plan on doing more engine mods down the road and you have the cash, you might as well go ahead and get the PC or U5.9(there are a few topics on comparing the two, just do a search). But if your budget is limited just take the bike to the stealer and get the trimmer bumped.