You need your MAF tuned. Your intake ducting has changed from the donor car, and/or you have a larger MAF housing. Either one can cause issues. Your long term fuel trims are telling you that you need 20+% fuel added at idle to be at the ideal air to fuel ratio. You need that fuel to make torque, so you've left a lot of driveability power on the table right now, unless you've got an exhaust leak pre-O2's or a vacuum leak.
05 Quicksilver Twin Turbo GTO
08 GMC 2500 HD Onyx Black Twin Turbo LMM Reading spark plugs