Interesting findings. The roughness persisted until MAF harness changed out. Still had problem with loss if power. The mechanic gave it a smoke test (that I had asked the Chevy dealer to do and they refused), and sure enough, just as I had read on the forum a hundred times, a crack in the intercooler several inches long. I totally missed it when I was looking as it runs down a seen and partially hidden behind the grill. So as you have told us numerous times the intercooler was the culprit. Had to order the part so another week but finally have the answer after replacing many parts. Should be back to full power by next weekend. At least I also found a mechanic I can trust, will never go back to the Chevy dealer what a rip off!