We have a 2015 Tiffin 37PA with an ISB 340 Cummins. We drove to Gaffney SC for some warranty work on frame and on the way down from Maryland we averaged 10.5mpg. After they did the 12 month service on the coach on the return trip I was surprised to see 11.3 on the fuel flow meter. Towing a 2002 Honda Accord V6 and keeping speed around 65.