Some of you do not remember the 105HP 292/300 CI inline 6's that were put into 25/35 series trucks back in the day! A BB had maybe 200 hp! I can get a 6.2 with a 400/400 motor or there about in a GM 1500 today! more power to tow than said truck can handle trailer!
With this said. GM any how, offers a std 3900 RA capacity. 3300 lb springs, plus the 600 lbs of unsprung weight in the axle and tires. The High Tow Payload Package, offers a 4300 lb spring pack, plus 600 lbs unladen wt, total 4900 lbs rear axel capacity, plus 3.73 gear sets in the 1500. Very similar upgrade to the SW 25 vs 35 series trucks. Do not recall if it has an 8.5 or 9.5" RP in the rear. Needless to say, if you are towing a lot, worth it if looking at a new factory order, or can find one on a dealer lot.
I believe Ford has a similar option. I have not heard that Dodge does, as they seem to want someone to go to the 2500 model. No in between models. Not positive about Toyota or Nissan if they offer a similar pkg. My swag is they do not. I am sure there is a person that knows these other brands that can correct any mistakes or thoughts I have.
I've actually been toying with a 1500 GM with this option with a 4.3 V6 if I can find one. As I really only need to haul 2000-3000 lbs with a truck today, tow 6000 lbs usually less than 20 miles. A 1500 properly equiped with do this. Along with getting double the mpg as my current 2500. 2 more gears in trans.....better options for my future needs. If I need to haul more weight.....well the 6 ton capacity Navistar does the truck very nicely!
Marty