For the money you would spend trying to get more mpg you can buy a lot of gas.
Not to spoil the fun, but Rustydagger hit it right on the head. Think of the money you saved on the purchse and how much (how long and how many miles) it would take at even 5 mpg better to get a return on a higher priced rig.
This leads me also to say that you MUST choose your mods, repairs and every dime spent wisely. If it is not a reliability issue, consider how long it will take you to recover that expense in any returns you might have in a potential increase in mileage.
Does that make sense? Other than just saying you have a truck that will get 30 mpg and the cool factor and attention that might receive from a limited audience. For example, even a rear end gear swap at say $500; how much fuel could you purchase for that price and how long would it take you to get that back, now having a possible 3mpg improvement.
Know what I am saying? So FREE is important. This will require some creativity, guts and a unorthodox approach. But be brave, ignore the "haters" and just try some of these. Keep a log and see what works and what doesn't. Some of this will require "fine tuning" as though it may seem logical, sometimes these things don't work out in the real world and require adjustment. Like jetting, gearing, etc. Like cracking a safe, every driver, environment and route holds its own unique combination.
But, to chime in because I am also a sucker for fun stuff like this;
As mentioned before, up your "overdrive" with Taller, skinny assed tires. Look around for some other wheels that may fit that are mass produced from another vehicle (if possible) and swap them on. Or, keep the wheels, and run skinny, tall, hard compound tires aired up to the moon. This will also make it easier to steer when you pull the belt off the power steering, the A/C and then also toss the compressor (weight). Look around and see if you can find underdrive pullies as well. You may find one off a Chevy small block and then re-drill it to fit the crank bolts. Take some measurements and see what you can find. Those are damn near free.
Then, make your own "aero" Mooney Salt Flats style wheel covers. Rather than expensive spun aluminum, cut the bottoms out of some discarded 5 gal paint buckets, spray paint them up flat black or Neon Orange or whatever floats your boat, then drill a few holes in them so that you can "Zip Tie" them over the top of the steel wheels.
BAM ! Instant Aero covers!
Then find an old plastic bed liner that blew out of someones truck on the side of the highway, take a jig saw or sawzall to it and fit it underneath the engine compartment. Obviously leaving cut outs for the exhaust, etc.
Tinker with it until it runs from the front bumper to the rear of the trans to smooth out the air flow underneath like an F1 car. This will help serve as a skid plate when you slam it on the ground with your home brewed lowering kit.
You may have to add some holes, depending on your seasonal temps and how much air is then trapped in the engine bay that can't get out. But, if you leave the rear of the flat plastic sheet about 4" lower under the cab, it should flow out fine. Just watch your engine temps and experiment especially since your water pump is spinning at 3/4 speed and you have a tiny import car electric fan on it.
You may have to also drill some oval holes in the hood just before the windshield. This is good, as you will have removed the wipers, radio antenna and switched to tiny rear view external mirror. The air blowing out of said holes will help clean the windshield in a downpour.
A high flow air cleaner filter will also help. Or hell, just remove the filter element and stretch a section of old panty hose over the open air box lid.
Synthetic fluids will give good returns. Engine, Trans and rear end. Just put a catch bucket under said underbelly pan to catch all the run off, as in any older vehicle, synthetics will just flow past all the old cork style valve cover and oil pan gaskets and seep everywhere else. Again, watch out, because this stuff is pricy. Find a friend with a newer vehicle who changes their synthetic oil waaay too early, like most do. Offer to do a "free" oil change, if they supply the fluids (if you know they have good synthetics in their rigs already). Surely you can spin on a new filter and run it out a few more thousand miles.
Hit the local "Pick Your Part" style junk yard. I believe earlier Hyundai electric fans come with metal shields that will fit and can be adapted easily to the smaller radiators. You can get the metal shroud and fan assembly in one piece, that simply unbolts and unplugs in a tidy little unit for cheap.
The mighty "Leaning Tower of Power" Slant Six is unstoppable, even with hand me down oil, limited air flow and a pair of Granny Panties doing the air filtration. Trust me.
Instead of putting a heavy wooden bed back in, why not just stretch some chain link fencing around a metal frame and use it as a bed floor. Functional, light and aero.
Also kill the motor at red lights and never, ever allow the engine to run if the truck is not in motion. Idle = Zero MPG.
Then take EVERYTHING out of it that is unnecessary to save weight. No tools, crap in the bed, bumpers or even change in the ash tray.
Learn to drive playing the "coasting game". Ooze up to speed, time your red lights and draft like mad behind any larger rig on the freeway.
Lol. Awesome. Have fun and good luck! And remember, perform these mods at your own risk. You may cut into Prius sales if you do it right.
