A slightly different approach, but you could get your wife a Durango or Grand Cherokee and then switch vehicles with her on days you need to tow. This assumes your wife is comfortable driving a larger SUV. If you did this, you could drive whatever you want every day.


Edit: I don't think you will find many older full size trucks with gasoline engines that will get much more than 15 mpg running empty. If you want to get over 20 mpg, you will probably have to get a diesel or a fairly new truck. Diesel engines save fuel, but cost more in other areas. Newer trucks are nice, but the fuel savings may fail to offset the depreciation on a truck that is not driven very often.

When towing with older gas powered trucks like your D100, I've frequently gotten around 8 mpg. It depends a lot on what you are towing and where you are towing it. I had one truck that would get 9 or 10 mpg towing. Another one only got 6 mpg on one trip, but that was towing a large, heavy camper through the mountains.

If you want an overdrive transmission and want to tow with your D100, I'd find a 5 speed out of a 1990's 2500 truck. Those have a lower first gear ratio than your 833OD and have an overdrive. A 5 speed would cost a bit more, but having that lower first gear would be real handy when starting off on a hill when you are towing a heavier load.