Update: Gallops were caused by two things. One was a voltage issue form the PCM I believe, but effectively was causing the MAP to die. We warrantied a MAP twice before it stuck (I see I mentioned that part already).
Second issue was an air filter line was falling out or had never been correctly installed when the filter got an upgrade - literally had no clamp to keep it from falling out of the air filter. It's finally properly installed to the filter (it's the smaller one going to the oil/intake manifold area, made of rubber, not the two big plastic air filter tubes). That made all the difference in the world -- think it has not been connected since Fall 2016, no wonder my mileage was terrible.
Ok, so eat your hearts out, even with the extra weight (250 springs, 250 lb bumper with class IV hitch, etc and oversize 31.5" tires on 15" rims and 1/2" spacers pushing them away from the frame for clearance), the truck gets about 14.6 mpg in the city and on the highway I'm somewhere in the 16-17 mpg range on long hauls with nothing in tow.
Yeah, happy about it. Slowly getting there.