They seriously can't figure it out? That's quite odd.
Though, maybe you need to find a shop that has a smoke machine and have them look for vacuum leaks. I gotta think they'd have checked plugs, wires, injectors, and rocker arms for movement, air filter for clogging, compression, etc. So that would mean something is wrong with the mixture.
If they didn't check any of those things, then you need to go to a better shop..... I'm reluctant to chip in further...
'09 PSM G8 GT - OPG Intake, DOD-Delete w/ Stage 1C 218/229 .600 Lift 117.5LSA, Kooks 1 7/8 Mids, Solo Axle-Back w/ X-Pipe, SuperPro Bushings (Front and Rear). BMR Sway Bars (Red)
"If you want to criticize someone else's work, be sure that your own is in order first."