At 317,000 miles on my Gas 2014 Promaster i averaged 19.4 mpg.... doing 68 to 69 mph...
At 39,849 miles on my Gas 2017 Promaster i average 19.3 mpg..(body 15 inches longer) doing 68 to 69 mph ....
Side note slow down alittle ... find your Vans Sweet spot ... keep extra money in Wallet...