What are you towing that requires 4. 10 gears?! I've seen A LOT of weight easily towed by 3. 73 gears. My 5th wheel is "only" 13k pounds, and I forget it there. My buddy had the CA DMV register his truck for GVW of 35K pounds. He tows a backhoe and drilling attachments on a tandem dual gooseneck trailer. Total weight at the scales - 32,500 lbs! :--) :--) :--) Mild power increases help with this, of course, but not enough to slip the stock clutch on a 6 speed. He was running a Volumizer with 4 inch exhaust and an AFE intake. No he couldn't do 75 up hills with that load but 55-60 was doable. Just a little food for though. Also, try hangin out in the towing/hauling forum with the guys who tow regularly with their trucks and see what they think. Good luck!