I thought of doing the 3500 pickup with 1000ftlbs, removing bed and installing an aluminum flatbed, I felt like while towing over 40,000lbs, I might run out of rear spring, axle or tire load capacity. I also like the extra braking capacity on the 5500 and the 4.88 gearing. The high capacity 43,000lb towing package made it an easy decision. I also like the 19.5 tires and the extra 19,500GVWR.
GM also offered a 3500 dually with a GCWR of 40,000lbs.
No doubt the pickups with 1000ftlbs must be sick fun to drive.