My brohter has a 07 GMC Yukon XL that was doing just what yours is doing. They put heads on it, no fix, they finally tore it down and put rings and pistons in it. That has fixed it for now and it had around 65 k on it when it started. Also bought used as a GMC Certified Pre-owned. I think it took 4 or 5 trips to the dealer before they tore it down. I know of one other but it was in a Chevy Silverado z71 and it was a 07 NBS also, both trucks have the 5.3 with the fuel management systems. They should fix it because they know that year model had that probelm. I might would try another dealer if one is close by.
