I get from under 5 mpg to over 6.5 mpg, depending upon... things... which I don't know what they are. One time on a trip from Butte to near Boise I got 6.8 mpg going down I15 to Rexburg, then on US20 to Mountain Home and filled up at the Boise Stage stop. Several trips I have got under 5 mpg. My estimate of mileage over the 12,000 miles I have put on this coach is between 5 and 5.5 mpg. My toad is a 2002 Chevy Avalanche which weighs in at just over 6,000 lbs. The coach and Avalanche weigh over 48,000 lbs when full of fuel and water. Most of the 12,000 miles have been when pulling the Avalanche. I usually drive from 60 to 67 mph on open roads depending upon speed limits, and I always use cruise control whenever possible. My foot is rarely on the throttle or brake in open road driving. I do most of my accelerating above 30 mph using the cruise control, and most of my slowing down to about 30 mph using the Jake.
The Marquis has an oil bath air filter and a reworked exhaust with a "performance" muffler. It makes a lot of noise when accelerating and especially when the Jake is activated for slowing. I would rather not hear what others are getting for mileage because it makes me wonder why I am not getting those efficiencies. I would rather hear what folks have done to successfully gain mileage. It appears the prior owner of my coach tried several things from air intake to exhaust changes to improve its mileage. I would enjoy getting 7 to 9 mpg. Oh well..... As they say, "If you have to ask, then you probably can't afford it anyways."