Look atat a GM with the 6.2 and heavy tow/payload packages. You get a 4950 RA, 3.73 gears. Few and very far between. You may have to order one. That is probably you best 15 series truck option for towing. Iirc a 12,000 lb max trailer.
But as noted, watch the payload to work with. The truck OP speed, for my family of 6, my tow capacity would be zero, nada, zilch, squat. As my family when kids weye teens, was 1200-1300 lbs. Add in a dog or two, rack for canoes, generator, firewood in bed, 800 lbs for hit h weight....2700-2800 lb payload minimum was needed!
Keep this in mind, said 15 series trucks may look good on paper, in reality.... useless.
Marty
