DP's are better off with manual trans so for your application with 5 speed that is one good thing, personally for a rig like that I would want more control over the secondaries and the DP will do that, add to that the right gear selection.
MPG > guess you could sqeeze the same out the same milage as a vacuum secondary if you keep you foot out of it.
Going out and dropping >400 bucks for a new one may not be worth the $$$ though ??? your call.