The DHP PCM for the V6, is about your only option (as in a 'chip'; note there is no 'chip' for a GA). Don't believe half the crap on ebay.
Another alternative, if your keen and plan to do some more mods, is take the tuning into your own hands.
I purchased tuning software from
www.hptuners.com. This gives you pretty much free reign on close to 300 or so parameters (including the few that are modified by the DHP Pcm). DHP also has some software out there called a PowerTuner (
www.digitalhorsepowerinc.com).
Any of the 3 items above, if applied to a stock car, will help out. However if you plan to modify your car, you can actually outperform the stock parameters of the computer (quite easily on the GA). Depending on the depth of the mods you plan, should help you decide which item to purchase.
Good luck!