My average is still around 13 after the tune up. I don't have a commute since I work from home, so I do most of my driving in less than 5 mile spurts. The heads up display says my average speed is 15.2mph. So a lot of my runs, it never gets up to peak operating temps & it's all stop & go with traffic lights. I'm sure this affects it a lot.
I made one 30 mile run on the highway right after the tune up & my average then on the highway was 17.8mpg.

My '98 4dr is similar for short trips in cold weather. You will likely notice a significant improvement in summer. The hotter the day, the better my mileage.

11.35 today
 

I filled mine yesterday worked out to 11.3 mpg. Need for spring and summer to get here so I can get back up to 16-17 like its use to.

Thanks

I was getting about 210 miles per tank, whick was about 15mpg mixed city/freeway... New cap,rotor,plugs an wires an went back to 5-30 mix syn I'm sitting at 260 and still got a quarter tank of gas. Man it this truck a PITA to do a tune up on though

After 3 years of work I have my 95 Blazer 2x4 getting 22MPG highway and about 18mpg city. It gets 340 miles to a tank. It could probably go 360, but I don't like to push it that low.

With minimal work on my 97 4x4 it is getting 18 mpg hwy and roughly 15-16 in the city. It gets about 280 to a tank. I have done 320 once before. Sketchy lol.

Mpgs
 

I'm getting 19.5 with a multi cylinder miss fire and bad wheel bearings 4x4 2 door with a 5 spd. Do a lot of coasting to stops in neutral and shift at 2k rpm. Probably 75% highway 60mph and 25% city.

98 4dr 4wd LT new motor 17k ago all stock get about 210 a tank then light comes on. I'm averaging 17-19 hwy depending on speed, 68 mph seems to be the sweet spot for 19 plus mpg. I try running only premium non ethanol. E gas kills 2-3 mpg. I run at 70mpg + on hwy.

Update I recently added a in line Fitch fuel catalyst and this helped mileage with E fuel about 1-2 mpg. Not much difference on daily driving with it.

1999 LT, 4.3l, 3.73:1, 30" tires

Cruising at 60-65 mph: 17-18 mpg
Towing my boat on highway: 13-14 mpg (2,200 lbs)
In town: 12-14 mpg

I have done a spectre intake with a flow master muffler, 31 inch Big O Bigfoots, torsion keys and shackle extensions roof rack, full size spare, full size chevy tow mirrors, a tune up and spacers. I only get 10-11 mpg, any ideas what I can do to improve upon my mileage without removing mods? All on a 98 Blazer 4.3 4 door 4WD with 3.73 gears. Auto trans 4l60e

For one thing, your speedometer is not going to be calibrated for the new tires. According to https://tiresize.com/comparison/, a 31x10.5R15 compared to a 235/70R15 tire will have a circumference of about 10.7% larger. This translates into you traveling actually 110.7 miles for every 100 miles your odometer (which counts tire rotations) says/thinks you have traveled. This means your mileage could be actually about 11% better, i.e. about 12 mpg! Whoo Hoo! :-)

Also, you added tow mirrors and a roof rack that along with raising your rig means there is more air to push out of the way which matters most at highway speeds. (BTW air drag force is roughly proportional to the cross-sectional area and the square of the speed, hence aerodynamics are going to matter more at highway speeds and when lifts etc. are done.) You also have the 3.73:1 rear axle which will never give as good mileage as the non-4WD ones with highway gears.

Have you checked your mileage at different speeds? Mine will get better on legs over which the speed limit is 60 or 65 mph vs 75 mph.

Finally, if you routinely carry around lots of gear like extra tire chains, a high-lift jack, you will get worse mileage than if you lighten your load.