snow mobile trailers are not that tall, a boat has even less resistance, i would be disappointed with 7mpg
It may be the hemi only has highway efficiency in 4 cylinder mode the small added drag of a snow mobile trailer takes it out of the efficiency range .
Once 5.7 engine has a load on it running at maximum torque output at given cruise rpm engine may be going full rich and is pulling back timing to avoid pre-ignition.
A pent roof combustion chamber 4-valve with continuously variable intake and exhaust cam timing can still maintain a leaner mixture and not retard timing so much under high torque loading (i wonder how the RAM v6 would do pulling same trailer).
I learned this with my 1989 Taurus SHO, the Yamaha 3.0 v6 would pull a 21 foot boat up the steepest hills on 94 going 80+ (when i was young and stupid) in top gear without slowing down, it even had decent acceleration left.
At the time my 1997 f150 with 4,6 v8 would drop out of overdrive and feel sluggish at only 70 going up same hills slightest attempt to accelerate would downshift to 3rd gear
The Hemi is a push rod 2 valve engine which once one lays into the throttle cannot hang with a 4 valve engine efficiency wise.
I found that with the Tundra 5.7 if i set the cruise control at 80 it never dropped below 15 mpg ( a lot of hills and head wind closer to 13mpg)
A cop wanted to buy my Tundra because he cruises at 85 mph any GM gasser he drove never got above 11 mpg at that speed.
very happy with my 6.7 2wd though have yet to see less than 22 mpg at 75 cruise
