You need to do some number crunching to figure out where the break-even point is going to be if you go with a diesel. That few of miles is not what a diesel is meant to do. A 15mpg diesel vs an 8mpg gasser, over 5,000 miles in a year, will save you $93 per month in fuel costs, based on today's prices (unleaded @ $3.40, diesel @ $2.80). A single repair on the diesel will wipe out all those savings, for many months. Everything you touch on a diesel costs much more than a gasser. Dual batteries, turbos, injectors, injection pumps, 14 quart oil changes...it goes on and on. There is nothing economical about these trucks--they are only less expensive to operate when compared to gas trucks that are being used hard every day, lots of miles over a long period of time.
Plus, I don't think this disparity in fuel prices is going to last. I hope it does, but have my doubts.