I've said it before and I'll say it again, the Sprinter inline 5-cylinder diesel is a sweetheart of an engine, with "power" all out of proportion to it's 154 hp rating and lots of examples of 300-500K miles before major engine work, and reports of consistent 20-25 mpg fuel economy. The V-6 diesel in the newer, NV3 version is smoother and drives less "trucklike," but appears to be down a couple mpg compared to the five. The V-6 hasn't had major reported problems, but hasn't been around long enough to get the same reputation for reliability.
But it's still not a big 'mericun V-8. One way to help, though, is to splice the adjustable diesel tuning module that The Sprinter Store sells into the engine computer. I (and many others) have done this and found it to be a very useful modification and the biggest advantage shows up on hills and when towing. My Sprinter, at 8500 pounds, is as heavy as a SRW unit can be. On my first, no module, trip across I-80 in Wyoming, the Sprinter took most of the big grades in the low 50s in third gear. After the module, the same grades were upper 50s and fourth gear, more often than not.
So it's not a powerhouse, but it is pretty capable (with the towing capacity never less than 5K and up to 7.5K on some versions) and would likely do the trick if you weren't expecting too much speed. By way of comparison, my Sprinter is considerably quicker than my 7000 pounds of Series 80 Land Cruiser, but not as quick as my 7000 pounds of regeared EarthRoamer Jeep Wrangler.
In any event, my experience is that most all Sprinter owners are very fond of their trucks, so I'd encourage you to look into getting one. It's undoubtedly the easiest van to drive (largely from it's narrowness), has by far the best seating position, and you can stand up in them, which is a huge advantage.
