I hooked onto my 11.6k 5th wheel on the weekend with my stock '03 duramax/allison and was not as impressed as I was hoping to be. I was pushing a bit of a wind and the truck would not hold the speed limit - 100km/hr (62mph) in 5th. When it would drop down to 4th, RPMs would jump to about 2800 and fuel consumption according to the dash readout would go from about 10mpg to around 6. If I stepped up the speed to 110, it would hold better, however it would still drop down on any bit of an incline.
I believe the truck has a 3.73 rear end.
Would a programmer help? Intake/exhaust modifications? I really want to tow this trailer comfortably in 5th at 110km/h, and I was hoping for more than 10mpg. My old 6.5 used to pull it OK and it would get over 12!

Slapshot

A programmer and larger free flowing exhaust will help your LB7 considerably, especially if your LB7 is one of those with a CAT. Have you upsized to larger diameter tires as well? This can affect your towing ability as well. JJ :)

I have noticed the same problem. Adding a performance mod will help. Driving a little faster also seems to limit the down shifting a little.

You will also need to keep an eye on Exhaust Gas Temperatures (EGT's) Could cause a turbo problem, if not.

An Edge "Juice with Attitude" has a built in EGT gauge.

I agree with Max Owner, the juice/attitude helped my towing considerably, although I never really had any problems with it stock. The juice just gives it that extra umph.

Dan

I don't tow a 5er, just a 22' trailer, but have towed between Las Vegas and Flagstaff AZ (through Laughlin) and up to Mammoth Lakes CA a few times (both can be hilly). After at least 10 tows long distances like that, the best I could ever get, at any speed, was 10mph. over the course of the trip. My rig is all stock. When I get into the hills, I turn the OD off to keep the rpm up higher, thinking that I get more boost from the turbo, and therefore more power, and I'm in no hurry so I'm not that excited about running 70mph uphill.