I have an 08 as recently have had power loss and gas mileage loss has auto trans when in low end of what I guess is overdrive and u accelerate it has a biggish vibration and poor exeleration turbo boost fine maybe more than normal and extremely worse if ac is on while idling has somewhat of a miss and don't through any codes started maybe a month ago and has gotten worse starts doing it around fifty and stops a little over sixty but even in passing gear take off is poor to what it use to be any ideas

 

Welcome to the site, check the air filter and the MAF sensor

 

Welcome to the site!
If you can't find that it's a simple problem.
have you checked the oil...is it burning oil? does the oil have a strong gas smell. or milky?
Is it smoking? Check the plugs, also a compression test.

 

I have changed the plugs there is no smoking or oil loss air filter looked clean ad I blew it out with air not much dirt or dust came out of it

 

Since you have moved the air box make sure your mass air flow sensor is hooked up. When I repaired the wooly worm on mine after the walmart mechanic broke it, the car did not operate quite up to snuff and I found the sensor connection, while it looked like it was plugged in it was not quite tight.

Just making it click cured my problems.

My daughter was using the HHR and decided she should have the oil changed since the oil life thing in the DIC said it was down to 20% oil life. The dude at walmart said he was just checking the air filter as part of their service when they do an oil change.

I suggested he go back to walmart mechanic school and learn how to take stuff apart without breaking it.