I bought my father's 83 Ranger 2wd,short box, 2.0, 4 speed stripy in 89 after he died. It had 3.08 gears and 195/75r14's, didn't have enough power to pull it's hat off, and got low 20's with me driving carefully for mileage- in the NH hills.
One note- lower gears means higher numerical gears- 4.10's would be lower than 3.45's. Maybe because top speed would be lower with 4.10's, but that's how their defined. With your 3.45's in overdrive (approx .70:1), your final drive ratio is 2.4. If Texas is as flat as I think it is, that might work, here you'd spend your life in 3rd and 4th gear so going to 3.73 or 4.10 would be apt to increase mileage.
An early Ranger would be lighter and that would help mileage, as would burning 100% gasoline instead of E10 or E15.
I have never owned a vehicle that I couldn't consistently exceed the EPA mileage estimate.
I like your credo "Never give up". Remember, it's not being stubborn, it's being persistent and determined. Stubborn is what people without discipline call it.
Another thought. If you're up for a teardown, the 2.3 in Pintos, Mustang II's, and fox bodies used to respond well to planing the head to boost compression- up to about .030". You'll have to get an adjustable cam sprocket to correct the timing and forget about 87 octane gas.