So I been on the GM V6 CLUB Facebook page with the Aus. LLT and LFX owners and some are actually using a small piggy back. There are two the Haltech and MoTec being used. With Haltech being the preferred one as it allows more features. It's mainly only supported overseas but found two dealers in Arizona for the Haltech. The Haltech PS2000 is their flagship model and been reading up on it. Looks promising but according to the owners you need a VERY good tech, the cost of the unit that is selected, and about $1500 to get running right. They have been using it to tune their boosted cars not N/A. Now to win the Lotto to see this in action lmao!!
http://www.haltech.com/
http://www.motec.com/aboutecu/ecuoverview/