I have a 2001 Suburban 1500 with the 5.3, towing package, Prodigy brake controller and Curt WD hitch and my 22 ft 2009 Wildwood X-Lite at 3650 dry weight is more than the Suburban comfortably tows. So much so that after a 5 week 3600 mile trip last summer from Minnesota to Vermont and places in between we bought a smaller trailer. The combination of weight, wind resistance and hills it just wasn't a pleasant experience. I think your calculations on paper are fairly close to correct but on the real world highway if you buy a trailer sized to your trucks max towing you will be disappointed in your towing experience.