Fryartruck

In my travels, the overhead gives a good, GENERAL overall estimate - then you discount it 10-15% for reality. The only real way to calculate this is on paper, which I will do.

We're taking a 2800 mile trip soon, I will update everyone by the time we get back. I'm pretty much thinking my mpg's are gonna be in the 12-15 range with pulling an 11,000# fifth wheel.

almost forgot: 2003 2500 CTD auto 4.10's long box 2wd silver cloth QC

GMScott

I too use the overhead for a general estimate plus a baseline idea of the quality of fuel that I just bought. Poor quality fuel will lower my AVG. M.P.G.'s on the overhead within 100 miles, with everything else remaining the same, such as wind, altitude & terrain. My overhead usually shows .1 to .2 m.p.g. more/higher than my actual m.p.g.'s. I have a digital fuel monitor that came with the TransferFlow aux. tank which monitors both the fuel in the factory tank & the aux. tank.
I don't know your driving patterns or what type of terrain you're gonna be driving but I think 12-15 m.p.g.'s is wishfull thinking towing an 11,000# f'ver. I usually cruise @ 75 m.p.h. with the cruise control and when I have that kind of weight will struggle to get into double digits. I've tried slowing down, even to 65 m.p.h. and still can only squeak out a bit over 10 m.p.g. Since I'm working while towing, the 1 m.p.g. I gain by slowing down is not worth the extra time I have to drive over a 1,300 mile trip. 122k miles on the clock so mine should be gettin' pretty close to being broke in!!
Anyway, have a safe one and enjoy your trip.

GMScott

OOoops, didn't see that you're driving a 5.9L. I thought I was in the 6.7L forum. Ya just might get that kind of m.p.g's even with the 4:10's. My 04.5 had the 4:10's and it got fantastic fuel mileage compared with my current 6.7L.