I do a set of pistons about every week. It's oil consumption, rings are stuck! Not to mention all the lifter and camshaft
issues too.

 

Like scooter said oil consumption. PRIMARILY on 07s done a few 08s though. ONLY on the DOD/AFM engines. GM has us do a top end clean, replace the left valve cover and then install a baffle in the oil pan to shield the spray from the AFM pressure relief valve. That usually doesnt fix it if they have been sucking oil for too long because the oil control rings get stuck causing oil consumption. If your curious the valve cover is for excessive PCV ingestion into the intake.