Our Grand Cherokee is factory rated for 5000 lbs. total weight, which is comfortably below the dry weight
of our 177, and we (generally) travel with empty tanks and not a lot of stuff beyond the normal camping gear.
We seldom travel Interstates, so 70 mph is not as important to us. On our way home today from a couple
of nights out, I was cruising along comfortably, watching the road and the scenery, when I discovered
we were doing 60 mph at 1500 rpm! That translates to between 13 and 15 mpg- OK by me- with no
apparent wiggle, wobble or strain.
Our Jeep has the 4 liter in-line 6 cyl. engine, (2 wheel drive). We saw a trailer at the campgrounds
that had to have been 30 feet, maybe more, being towed by a Grand Cherokee 3.5 liter, but 4 wheel drive.
I forget the trailer make, but it was touted as "super light weight", whatever that implies.