There are plenty of threads on what to do for a tune-up if you search the forums.

I've done the work for you:

https://blazerforum.com/m_25319/tm.htm
https://blazerforum.com/m_11001/tm.htm

But, this thread is about gas mileage, not tune-ups.[&:]

 

On the A/C reply 3 posts up. I have noticed a difference with my bravada and I keep records of mileage, gallons of fuel, and the type of driving that was done since the last fillup, every fillup. With as hot as it had been the previous two weeks, there was a noticeable difference in my fuel mileage with the A/C off, but like I said in another thread, some of that could have been my laid back driving with the windows down enjoying the weather. So I cannot attribute the entire ~2mpg to having the A/C off and my driving habits didn't change enough to be responsible for the entire difference either. Not to mention that my 17.4mpg tank included 7 trips between my new and old house which is about 5 miles one way and one way of each trip was loaded to the gills with stuff being moved.

As far as a good tuneup, a normal tune up consists of new plugs (AC Delco Double Platinum recommended), new wires (I recommend either AC Delco wires or Napa Belden Premium wires - both are excellent), and atleast check the cap and rotor. If either shows signs of wear or carbon trailing, replace them. If a tune up has never been done, it may be time to replace the upstream O2 sensors, but if your mileage isn't real bad, I'd do a general tune up first, then keep track of your mileage and see how it is after. But yeah... That isn't really meant for this topic.

 

yyyep...did tune-up. AC Delco Plats, MSD spark plug wires, distributor cap and rotor, PCV Valve, K&N Air Filter, top radiator hose, radiator cap, 195 degree failsafe thermostat,, fuel filter....yea actually...heres all the stuff ive done.

Replaced
- spark plugs (AC Delco platinums)
- spark plug wires (MSD)
- PCV Valve
- top radiator hose
- radiator cap
- 195 degree failsafe thermostat
- mirrors
- head lights (Silverstar)
- floor mats
- bug deflector
- air control ****
- cab lights
- wipers (Triple Edge)...they suck
- in-dash lightbulbs
- brake rotors
- ceramic brake pads (Hawk Performance)
- air filter (K&N)
- fuel filter (Fram)...don't buy....complete junk
- vacuum lines
- 4X4 vacuum swtich
- oil cooler hose assembly
- caliper bolts
- caliper bushings
- shocks (Monroe)
- distributor cap
- distributor rotor
- CD player (Pioneer Premier)
- tires (GoodYear Wrangler radials)

Fixed
- door panels
- AC compressor
- passenger seat
- windshield wiper sprayer motors
- anti-lock brakes
- 4x4
- cleaned MAF sensor
- cleaned throttle body
- vacuum leak

I'm sure theres more...

What is still left to do
- replace catayltic converter
- replace O2 sensors

 

Quiet a list.

If an O2 sensor fails the pcm will go into defualt mode. Your gas mileage will suck, but she will run. try disconnecting the O2 sensor and see if anything changes. If not, might be time to replace them.

The typicall culprits for low fuel mileage is a dirt air cleaner, and a dirty fuel filter. After that, tune up. Dirty air cleaner is the number one thing to kill fuel mileage.

Also check your tire pressure.