The tow rating he states is pretty accurate. My '06 CTD, 2500 is 4X4 but close to what he is quoting and mine is not a mega cab. GVW on my truck is 9000. The diesel eats a lot of pay load. Be aware too that the hitch rating on that truck is 1200 lbs.
My hitch weight is right around 1200 lbs and, while I am almost 1000 lbs below my rear axle GAWR and below the front GAWR, I am right at max truck GVWR. My TT weight is close to 10K. The truck handles it very well but, I wouldn't want more TT than I have.