I've posted several times here that I think the vast majority of the D.C. food trucks are, alas, not worth the $$. Those that are decent tend to charge much more than comparable trucks in NYC. (The Jose Andres Pepe truck is a prime example -- very good sandwiches, but they cost as much or more than if you got them at Jaleo itself; they should be considerably less, but I'm sure they're charging what the market will bear . . . . Salt River Lobster, too.) In the past I've touted Sang on Wheels as an exception -- very good value for often-excellent, nongeneric food (albeit somewhat unpredictable).
I've happened upon two other trucks in recent days that show great promise, at least based on a single visit -- ChefDriven, which although not cheap is putting out excellent food -- actually worth what they charge -- and, believe it or not (I didn't, but it's for real) . . . http://pbjtruckdc.com/. The "Spicy Pig" was really good, and very generous, and only $6. If you're not too embarrassed to be seen standing in line, check it out.