Getting Horrible MPG's

[spartan]

Recently picked up this pretty beat S14 and i am in the process of restoring it to sound mechanical performance.
It has a SR20DET all stock as far as i know except the GReddy intake manifold.
I've been getting only the worst mpg, i can smell fuel in the cabin when i have the windows down only, I read a similar thread on here but there are so many different possiblilties but never had a solution posted.
I drive about 2k miles a month so i drive between 55 and 65mph 90% of the time so save on fuel, but i still get just horrible results.
This morning for example i put in $40 91 octane Cheveron an it put me at a hair above half a tank, drove 32 miles to work and now its just a hair above quarter of a tank.
I havent noticed an fuel leaking but it could be evaporating quickly.
The tires are huge (F235 R275) but i know that cannot make it that bad.
I'm going to try and get a oil change and replace spark plugs done asap but money has been very tight, so hopefully next week.
Going with NGK Iridium IX spark plugs and 5w30 full synthetic motor oil

I have read it can be a dirty fuel filter but it only smells like fuel inside the car when windows are down, unless that has nothing to do with it.

Ive also read might be an injector not sitting right.

and also a fuel leak some where.

I want to take it to a dealership and just have them look at it not have them repair it cuz i know it would be damn pricey.
Any other opinions you can share i'd greatly appreciate it