Ok, on the gearing, Mike is wrong (no offense)... the ONLY guaranteed ratio setup on a Ranger is a 2.3L 4x4 truck, those only came with 4.10:1 gearing, the rest are a complete crapshoot... my '90 came from the factory with 3.08:1 gears and 195 70 14 tires which was a fairly common setup, it was an annoying setup but common...

. Depending on trim level, transmission, tire size, and all sorts of other things they put most any ratio in these things but unless it was 4x4 it'll most likely be taller gears than lower... the chances of 3.08 or 3.45 gears outweigh that of 3.73 or 4.10.
That said, my Ranger has been through many iterations, the first step was 28" tall tires (biggest I could fit stock when it was a 4x2) which I ran with 3.08 gears for a while, I got the same 26mpg average that I did with the 25" tires but I was in 4th gear on the highway instead of 5th, swapped to 3.73 gears with the same tires, great match if I remember right (this was in 2004, it's getting fuzzy), and I think the gas mileage stayed the same until the engine started going south (one cylinder was a little low on compression, went down to 23mpg). Was like that for a while then swapped to a 4x4 frame with 31" tires and 4x10 gears and got 19mpg no matter what I did. Then did the turbo swap and got 9-18mpg depending on driving style

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These engines don't care how fast they are ran, pretty tough (the engine issues I mentioned earlier were at I believe 150,000 miles), you'll get the same gas mileage no matter what you do as long as you keep the engine speed below 3000rpm which is the point at which the fuel system goes out of closed loop and runs richer. If you keep the cruise rpm between 2500rpm and 3000 you will be where the engine wants to be.
On the turbo swap, with what I've gotten and if you adjust things for if I had done everything right the first time I have about $1000 into my swap, that includes the $600 complete turbo engine and the little nickel and dime stuff. If I was to do it again I have everything needed in my garage and would have maybe $500 in another setup... If you are wondering about the power I have now, I'm lifted around 6" on 35" tires with 5.13:1 gears, mid April I went on a camping trip with a smallish enclosed trailer, 7000lb combined weight (maybe 7200, didn't weigh on the way there just on the way back) going over a mountain pass and I was able to hold 55mph up the hill both ways, took 3rd gear but it did it, could have gone faster but I don't like driving for miles at 4500rpm at 12psi, 55mph was 5psi

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Ok, I think I'm done writing a book now...