Looking at a 260 hp 5.9 Cummins in a super clean 2001 Expedition 34N that weighs 18400 dry. How much of a slug is this setup and will the transmission hold up to more power?
5.9 Cummins with the Allison trans is one of the best combos ever made. You can bolt on some parts to add some hp, but you probably will not need to.
Your rig weighs 18,400 pounds. A full size pickup with a 7,000 pound trailer weighs around 14,000 pounds. Not that different, especially with the right gear ratios in the MH.