The hitch on many of the sprinters is rated at 3,500 pounds. The curb weight is around 9,900 lbs, so well within the GCWR.
Your defense of gas engines reminds me of a story. Wow, this is 15 years ago! I was working with a horse rescue and I had a 1997 Dodge Ram with a Cummins. 180 HP and 420 lb/ft of torque. I was asked to help transport several horses and when I arrived, there was a guy with a Brand New 2000 Dodge Ram with a V-10. This guy kept telling me what a mistake it was buying a diesel when his V-10 has more HP and torque blah blah blah. 300 HP! He must have said 300 HP about a dozen times.
Well, we both had 3 horse trailers and were given 3 horses to transport, and I was going to follow him. It was a very warm day in Southern California, and we got out on the highway and we started to encounter a large incline. We were doing 70 MPH up to that incline and then started slowing down. At 55MPH, I had quite of bit of throttle left, so I pulled over and passed him, albeit slowly.
When we finally arrived at our destination, he kept saying there must be something wrong and he is taking it back to the dealer. I simply said "It isn't horsepower, it is torque at RPM."
When you buy a towing vehicle based on horsepower, you have fallen for the marketing materials. You want to buy one based on torque at RPM. The Sprinter is 243 lb-ft at 1600RPM. The V-10 305HP is 420 at 3250 RPM, which drops to 277 lb-ft on a 70F day at 10,000 feet on a much heavier vehicle. To achieve that much torque, the gas engine will have to be in a lower gear which means going slower.
In addition, we plan to put around 50K miles a year on this vehicle, so the better fuel economy would save us about $5K over a larger diesel, or $10K over a gas engine. In addition, the longevity of the I5 is likely to save us even more money.
I didn't really ask for a diesel vs gas discussion, but thanks for your input anyway.