I turn the OD off when towing, also. However, I have the (crummy for towing) 3.08 rear end, so it's a no-brainer for me. I plan to switch to 3.73's sometime early next year. Just waiting until there's more resources to do the job (aka..money).

NCC

 

I will have to take some pics with the boat on it. I had an 01 Screw, went Chevy for 1.5 years in a Tahoe, really missed the truck so I am back.

 

I towed 5500 lbs with my '05 5.4 3v 3.73LS. I averaged 65 mph and I kept O/D on. The truck didn't downshift unless I got to a hill. I would have turned it off if it kept changing between 3rd and 4th.

 

I towed this 250 miles last week. Not bad, light, but the same crap uhaul force brake system causing it to buck a bit downhill and after light stops. 03 SCREW with the 5.4 and 3.73's.