A buddy of mine has a 08 Serria 1500 with the 5.3, 4 speed tranny. It was using about 2-3 qts every 3,000 miles. Went through the whole consumption test, they installed oil splash gaurds in the pan and other stuff which made absolutey no sense to me. Went through the whole comsumption test again. Still using oil.
GM finally came back with the solution of replacing the pistons, rings and knuckles (whatever knuckles are).
I'm thinking it would be easier to replace the whole motor. Oh, and the service manager said they have done two of these procedures already so they are pretty sure they'll have no problems. Yeah right. I'd be worried. This doesn't sound like something a dealership service dept should be doing. If I were him, I'd be trading it right back to them after they're done.
I thank God everyday my 2008 uses absolutely no oil. Amazing how the two trucks being virtually the same age can be so different. I drive pretty aggressively and he doesn't. Plus if I'm going below 35 I'll drop it down to 3rd almost always to disable AFM because it sounds terrible with Magnaflow duals. Maybe that's the difference.