So here is ,my build...is MPG where it should be?
 

2002 5.9
Stock Auto trans /w 3.55 gears
Quadzilla adrenaline
S&B Intake
blue chip vp44
gauge pillar with fuel pressure, always reads higher than 15psi
295/65/18 nitto trial grapplers
4 inch magnaflow turbo back with muffler delete.
stock turbo.
150k miles
Basically I am averaging 13 in stop and go and 16.5 freeway with no load.
Now the ECU has not been calibrated to the tires so I figured out a 7.6% less revolutions per mile from stock tires. Are these fuel numbers seem reasonable?
I was thinking about getting my valves checked. and checking for leaks in the intercooler piping. What Do you all think?

seems low to me, i get about that and im running 4.88 in my f550

Yeah that's pretty low mileage. I'm averaging between 14.5-16.3 mpg right now. That's with letting it idle for about 10 minutes since its been in the negatives the past couple weeks. Mines a 96' 3500 stick with 4.10 rear end. I'd definitely get it checked into

My stock 99 has been really low, like 11.5 lately. I think it's because it soo cold and my engine isn't heating up fully. That's on the highway mainly 70+ mph. Usually, it was much higher like at least 16 or more. I believe my injectors are stock with 206k miles. Does anyone know what injectors to use for straight out highway running that will seriously increase mileage mainly?? Thanks..

Oh i forgot i have Bosch rv275 injectors

RV 275's are one of the better mpg injectors, but that is a whole can of worms, there are many different opinions on which injectors get the best mileage.
I am leaning towards getting F1 mach 1.6 injectors

I don't know much about injectors. I think the bigger tires causes worse mpg, even though i didn't think they did