FreeLanceing,
We had the same Lance 915 on a 2500 Chev 5.7 gas ext cab LB 4X4 truck and on our 04.5 D/A CC LB 4X4 truck. Average mileage on the gas truck was 9.76 mpg with the Lance on as we keep logs. That was over a distance traveled with the TC on of 94,678 miles and 2 trips to Alaska and back from Grand Haven. One trip was 13,137 miles long and 9-1/2 weeks.
The purchased new D/A averages 14.4 over 29,156 miles with just the 915 on and 13.8 with our 2150 lb boat/trailer behind over 43,888 miles. The rest of the miles on the D/A were with pulling our 5th wheel or our TT. We almost never drive the D/A unloaded as we have other vehicles for that but it did get over 20 mpg highway the times we had.
As usual, donn0128 is full of beans on the payload of the GM 2500HD. It's not a Dodge/Ram 2500! You'll be fine with your TC loaded for a long trip to Alaska and even pulling your MC behind on a trailer if you want to. The diesel should give you 30%-40% higher mpgs over a gas engine and the fuel price difference is between 10% and 20%. Lots of savings with diesel on long trips and the engine just purrs slowly all the way and yet climbs grades without downshifting and having a screaming engine like with gas! Usually around 10% difference in Grand Haven. When we left GH on our trip last Sunday, gas was $3.45 and Diesel was $3.58 at Meijer. $3.89 to $4.05 here in Florida or about 17% difference! Just enjoy your wonderful trip and you'll want to go again!
You may have seen our red 04.5 Chevy D/A CC LB 4X4 truck with the 11'4" Lance on it around town as it's on late spring and all summer and fall and we use it a lot. Get dinner takeout and go to the river or the state park etc and eat and enjoy with our Siberian Husky. Also for Tuesday's concerts in Central Park, it's always parked in the new Courthouse parking lot and in the Piano Factory Condo's lot across from the Municipal Marina for the CG Festival and many other of the gobs of events in town. It's driven in town at least 4 days a week.
BTW, the shipping weight for the big optioned out Lance as printed on the shipper from Lance is 3872 lbs and the 2500 with airbags and 265/75/16 "E" tires and Rancho 9000XL adjustable shocks handles the load great. It's capacity is as much or more than the GM 3500 SRW OEM truck! GM only makes one chassis for the HD's and they are all identical.
The 2008 with the extra polution junk on it will usually get about 1-2 mpg less than the D/A 04.5 to the 07 classics (LLY & LBZ). The main thing to remember for good mpg's is to keep your speed under 60 mph (58-60) when loaded and coast to drain off most speed before using the brakes and avoid jack rabbit starts both for gas and diesel. The upper speed limit in Canada going to Alaska is 90-100 km anyway so that's a max of 62 mph. I think you may already know that!
What you nor anyone do not know but the previous owner/owners is how the 2008 D/A was actually used or maintained or misused. As an automotive engineer, I sure wouldn't ever put a programmer on a truck that certainly doesn't need it or any other vehicle either for that matter as it puts higher stresses on the entire drive train and for what? A very slight gain to one's ego?