As it turns out: Just a few months ago, we bought a nice '05 Suburban 2500 with the 6.0. There was no 7.4 that year, though the 8.1 was still available. The 8.1 with 4.10 axles did indeed get a 12K trailer rating, though the same 2527 pound payload rating as the 6.0; a 12K trailer with 15% tongue weight similarly eats…