Howdy, I have a 2008 GXL and tow a 3.3 ton trailer loaded with a roller brake tester and mobile play detector. I have a Scangauge II and average about 21 l/hundred with he trailer on. About 9.5 - 10 on the highway with nothing on the back and 20-21 with a 2.5 ton van. I ave a 50 mm lift and roof bars which probably account for at least .5 Cheers Skip