Memorial weekend trip of 539 miles roundtrip, southern Ohio to southern Ky., Evarts, Harlan County was mostly hills, SR32, I275, I75, 25E, Ky119, Ky38. Pulled 38' enclosed gooseneck w/ living quarters, 5 ATV's, and gear, real close to 22400# truck and trailer plus add on 3 people. Pulled great, plenty of power, temps in mid 80's to low 90's, air cond of course. Speed usually 67-70 mph hill or no hill. Mileage was 11.6 mpg, I'm happy! Lost the cat a month ago and under heavy load engine seems to pull easier, no diff under no to light loads. Last summer a 400 pound lighter load only ran 10.5 mpg with cat. Believe cat costs somwhere between .5 -1 mpg under heavy load. Does any one concur with my observation?? bob.............. Also now have a boost stick this summer to top off the Edge/Attitude that was on last summer.