[5speed5]

Here's a bit of an off the wall suggestion. How about a Chevy Caprice?
They're tow-rated to 5000 lbs with the 5.7L LT1 engine.

I had a '96 with 5.7L LT1 engine that got me 27-29 mpg on the highway regularly at 75 mph. (Chevy put some really tall gears in the rear to get that good highway mileage. To see what I mean, the tow package comes with 2.93 rear gears, while the standard ratio is 2.56) That's with no ecomods at all. Outfit it with some smooth hubcaps, warm-air intake, partial grill block, etc. and you could be seeing over 30 mpg. You could even get the Caprice wagon and have almost as much cargo room as a Suburban.

Of course, you'll need some studded snow tires for the winter, but with positraction, you'll be able to get through all but the biggest snows.