Why is my mpg so bad?? 2006 4.0 6MT

I used to have a 2nd gen 6 speed, it was bone stock with P245/75r16 highway tires, never drove faster than 70 MPH, meticulously maintained, under 50,000 miles, etc. It got about the same MPG. One really snowy winter it regularly got 12 MPG just using 4WD a lot to get to work, not even off-roading. That was one of many reasons I grew to despise it.

 

I kept track of my mpg since I purchase the mine in late November of 2016 and the worst is 12.8, best 23.9, and average 17.3. I don't like it, but it's a 4.0 Tacoma 4x4. Minnesota winters aren't nice to MPG. My Ultra gauge reads my average mpg a tenth or two higher.
Only change that may make a difference in my MPG in the future is I recently change my disgusting looking and leaky stock aluminum wheels with stock steel wheels. Tires are stock size.
It don't get that much worst MPG than my old 2 wheel drive 2.9 Ford Ranger and it was a manual.

 

only 106k miles, but ive also wondered if the fuel pump is starting to show age. it turns over a little longer than i feel like it should on startup, but it also might just be how long these engines take to start. not absurd by any means, but just a tiny bit longer

 

I have thought a lot about this too as mine is pretty similar:

06 6sp w/ 140kmi. E rated 265/70/16. OME 884 springs for 1.5ish in of lift. Stock bumpers, no armor, but with a reinforced topper. 13ish mpg city. Best ever is 18mpg on all highway tank shifting at or below 2500rpm at all times.

New: fluids all around, plugs, air filter, pcv, serpentine and idlers, etc. I have done just about every normal upkeep item on the truck and then some.

Not yet done: injectors, fuel pump or filter, 3 degree exhaust cam gears.

I have noticed that idling really eats gas. Any tank where the truck has idled for 15-20 minutes while warming up, seems to eat into it a lot. Also, we have been on winter gas since I did about half of the maintenance items, so my hope is that I get a little more back once it warms up again. I plan to do the exhaust cam gears in the spring (claimed to be good for 1-2mpg) and replace 16in E load tires and wheels with lighter weight 17in passenger tires and wheels (still oversized) in a year or two.

I had an 08 4runner with auto trans and dual vvti (our trucks have single) and it got 17-18 around town and 21-22 on the highway without really making an effort at it. It had p rated 17in wheels and tires too instead of the e loads. I think the 4runner auto had 3.73 gears rather than the manual 4.11 gears too. We have different 4wd setup too- 4 runner had center torsen diff, so maybe even that could have an impact. I still prefer the tacoma with the manual because I love driving a manual, but wasn't expecting such a drop in mpg when I got it.

 

Winter fuel is hurting the numbers a little bit. Some basic maintenance items might help: engine air filter, spark plugs, clean MAF, clean throttle body.

 

The next time I buy tires, I'm considering a 235/85-16 in the Falken Wildpeaks. I do believe the narrower tire will net me just a little more fuel efficiency. I also think that lifting a truck or having the front higher than the rear will increase your wind drag and decrease highway mpg.
I had an old GMC years ago that had the 4.3L Vortec V-6. It had helper springs in the rear and had a rake like a top fuel dragster. When I finally got around to taking the helper springs out, I swear I lost some mpgs.

 

I get about 11-13 mpg on my 6spd. Tires are 285/75r16 10plys. Plus the how much everything else added to the truck. And I have a drawer system in the bed. Just part of the game. 2011 trd OR 108k on it.