Poor mpg on a well maintained, k1500 burb

there's no mechanic in a can , I would never add any crap like that , try a non ethanol fuel , my 1/2 ton 94 GMC only gets about 13 mpg so that's not too far off , still get rubber on wet pavement so my motors not beat or smoking

I have used non ethanol, I would not think as much about this, except how consistent it is at 10mpg, after different fuels and parts. The up side is it runs great. it makes me think of some kind of limp mode. No codes, I would think anything that would cause a limp mode would also throw a code.

I had simi9problem went to delphi electric spider injection and turned with TOAD software now I'm at 15 to 17 hgwy. Also changing gear ratio to get to rpm quicker. Went k&n kevlar intake I'm getting as good as it gets. By the way 10mpg from a 3/4 ton is optimal

Also make sure your solenoids are disengaged in front axle is could be running your axle semi engaged or fully but you'd notice full engaged front axle.