I'm getting 14.2 avg which is about 1/2 surface streets and 1/2 hwy for my 12 mile work commute.
I now have 3K on a 2005 LLY. The only "real" hwy driving I have been pulling a 9000# 28' 5th wheel and getting about 10.5mpg between Phoenix and Payson AZ. About five 6% grades on the road at over 100deg ambient temp. Tried not to answer the highway because of not running unloaded but it did not like that. I choose 15-16 hwy only because I have yet to see anything over that.