I tow with a 6 cylinder...Cummins... If you can find a 94-98 12 valve cummins it is just about indestructable. You get around all the injector/injector pump problems of newer diesels. The 12 valve cummins from 94-98 has an engine oil lubricated injector pump, all other diesels rely on diesel fuel alone to lubricate. I have a 94 2wd, all mechanical, manual trans, and towing a 5x10 ramp gate in city driving i average 16-17 mpg per tank all towing all city, with A/C and an aftermarket stereo loading the engine.
It may be hard to find a decent 12 valve dodge but the efficiency and durability are second to none. I also get to skip emissions testing in my area. The 7.3 ford diesel is fairly reliable but gives up a few MPG to a cummins 12 valve.