Don't be heavy with the foot??
Plus all those other things they tell ya, correctly inflated tires, clean air filters, etc. Don't tote anything you don't need, to cut down on the weight (ya, I know, we need it all!
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We get 7 to 8 toting Tana. We can get 99 down a big hill, but ya gotta go up the other side (usually) and we only get about 3 going up. SIGHHHH
We use tow haul, take out of overdrive (you know, have that little yellow light on the dask board ON, as in disengaged, right??), and use speed control. Now, get in the big hills and we turn off the speed control and Al drives it up the hills, he is not here so I cannot ask him, I think it is like 3200 RPM that he tries to maintain on those big hills. Don't look at the speed, only the RPM's.
If you have the Allison, learn how to engage it coming down those big hills, let that monster ROAR! and brake you.
Get ready to pass anything you like on the road, cept a gas station!
Big Butt has that electronic stuff that tells you instant economy and all those fun things. I believe that we do the best at about 57 to 62 MPH, but that has changed a bit as Big Butt gets older and broke in.
We always said we got 7, but on the way from Virginia to Michigan in April, we were getting 7.5 consistent. Not sure why, we just grinned and kept on trucking. We took 81 north to the 70 over to Breezewood, the PA turnpike west to the end, and Ohio turnpike west to past the Toledo area. Even in the Somerset area of PA we were getting 7.5 and that really was a grand surprise!
Have a grand trip!!