I have a 2009 Hummer alpha with low miles.I bought it in June 2016 mpg was 18 highway! Had a mechanic put a spectre air system on,and tossed the origial stuff out.It is at the GMC dealer ,13mpg and low power on highway,this is an LS motor 300+go. Problem is there needs to be back pressure after the oxy sensor in tube before throttle body.2 different GM dealers diagnosis was same. Computer reads lean both banks because too much oxygen. Look at original tube out of air box, it goes to oval ,about 1.5 inches tall,4 inches long,then back to round into throttle body.Heres the back pressure the sensor reads.I wish someone made a K&N style system. Dealer measured air flow and found it to be off. This is a nitemare you can eliminate, keep original and buy a cloth square filter.

 

OEM air box, AFE ProDry air filter and AirDoc CAI since 2008 on 6 different Alphas and not a single issue. Not sure what your CAI looks like. Post up some pix please.

 

AirDoc intake, Spectre dry filter in factory (closed) air box.
Installed in 2010. NO issues.