I get up to 18mpg regularly with my 5.2.
Anyway I can get 14-20mpg in town with an 01 Dodge Ram 1500 5.2 v8 club cab. (summer time)
A few specific things if you can afford it a manual transmission can get you better than the auto, much better but you need to know how to drive the truck to get better with a manual (much worse if you don't).
With an auto like mine the 5.2 DOES NOT LIKE GRANDMA! It also does not like over revving or being floored either.
I own a scanguage and I can see I get better fuel economy with moderate acceleration, especially in town as compared to slow acceleration. Usually about 50%-70% throttle is best.
Next, in town you must COAST as much as possible on that same regard inflate your tires at least to the sidewall rating, mine are 50psi, I run 60psi in the rear 50psi in the front. If your roads aren't laden with 4ft deep potholes keep the tires aired and you will gain at least a mpg on that alone.
So on your 5.2 at low speeds you better either be accelerating or coasting, to maintain speed is very difficult as you need to overshoot speed let off the throttle and push it in a very small amount just enough to maintain speed or slowly loose speed, if you just hold the pedal in after accelerating your MPGs will be much lower. I'm not sure if its the dodge computer or what but I've noticed this behavior in multiple vehicles.
I don't know if you have a topper or a bed cover but if you really don't need either consider using the EPA proven HALF bed cover where the bed cover only covers the rear of half of your truck bed, that gains again 1-3mpg depending on your speed & shape. A sheet of plywood and some clamps might suffice for a 500mile test. Another option is to take an old useless topper and cut it into an angled topper, get an old tent and make a popup topper (look around ecomodder there are a few out there)
My technique in town is to waver the pedal (my computer is slow for some reason) then take off firmly, overshoot the posted speed limit by 5mph let off the gas then press it in just enough to barely keep speed (or just a little less) If I will have to stop quickly I speed up to about 20mph (or whatever I can get away with) and coast in neutral to the stop, sometimes less sometimes more depending on how far the stop is off. If you are in stop and go with a 5.2 you are basically screwed. Generally you want to coast down to about 10mph (ideally) before stopping at a light or sign because your mileage in Neutral with the pedal at idle at 10mph is about 14mpg (still better than 11).
The 5.2's love to drive up and down hillls at slow speeds, when I had the opportunity I got 20mpg, I would burn going up the hill let off the gas and just coast over the tops, coast down the hill in neutral my turns were timed so I could make them without braking (lights timed0. I knew the route really well and planned it out. If you can figure ways of getting the truck to coast through green lights that gains you a lot, even if it means driving a little slow.
Also if you are going to come to a stop and you don't care what the consequences are (if there are any) always shift to neutral when coasting, My truck burns 3/4 gallon an hour in gear 1/2 gallon per hour in neutral. Why dodge wants to rev the motor in gear I have no idea but this DOES waste a fair amount of gas, especially at stop lights.
That said I really wish my truck was a manual, sadly I know of no reasonable way to make it into a 5 or 6 speed manual.