The 4R100 behind the 7.3L suffered from poor torque-converter strategy combined with inefficient cooling to cope with the extra heat generate by torque converter being unlocked so much. A programmer like the Banks TransCommand (or even a torque converter lock switch) will go a long ways towards solving the root problem, and a larger cooler will shed any excess heat. The 4R100 mechanically is strong, and holds up great behind the V10. I gross as heavy as 25,000 combined, mostly mountain driving, and have 391,000 miles on my 4R100, and I only do fluid changes every 100,000.
