1998 Chevy Blazer Gas mileage

I keep trying to get better gas mileage out of my stock 98 chevy s-10 blazer but I don't seem to be getting anywhere with it. It has a re-man transmission in it, tune up has been done with new cap, rotor, plugs, wires, PCV valve, air filter, fuel filter and have ran 3 bottles of lucas fuel injection cleaner every other fuel tank. Oil has been changed to Valvoline synthetic and all other fluid levels and tire pressures are at proper levels. And I cleaned the MAF sensor w/MAF sensor cleaner. Doesn't seem to have any sort of vacuum leaks. The engine vacuum measures in steady at 16 in hg @ engine idle, 21 in hg @ sharp increase in RPMs and below 5 in hg @ sharp decrease in RPMs. No DTCs in computer. Having said all of the that I can't get any more then 14 mpg on the highway and city mileage is horrible. Any suggestions or solutions? Any help would be great