I have a 2004 3500 long bed dually with the 5.9 HO turbo. I've added a 5" turbo down pipe, eliminated the resonator, added a custom 5" in x dual 4" out muffler with dual 4" pipes. I've also added an Edge chip & keep it in step 1. An AFE air box helps. Mag-Hytec trans & rear diff pans keep things cool. An Empi 96 plate trans cooler w/ fan is in-line off the tranny for slow speed towing cooling. My short block was replaced (under warranty) at 7,500 miles. The automatic trans was replaced @ 11,000 miles (under warranty) & now it tows better than before, but I'm thinking about changing to 4.88's to make it easier still. I tow a 48' gooseneck trlr with this trk. When I'm coupled up, I'm 64' 10" long and around 27,000 lbs. so I've been told by Gear Vendors I'm beyond their recommended 25,000 # limit for their help. Anyone out there that's already running 4.88's have any advise for me?
I can tell you your best bet would be look into the US Gear underdrive unit. I have a customer with one on his F550 with a twin turboed Cummins. His GCW at the scales is 42-45K. He pulls a back hoe and an excavator. Shift perfect and you can use it in 4WD, with the GV unit its 2WD only!
