Axle Ratio Vs. MPG

I've seen people debate axle ratio and MPGs before and I was always convinced to get the taller gear( lower number) for better highway mileage because I do alot of it. 15-20K/year or more, a lot of it unloaded. but I plan on keeping my truck 10+ years and I don't know if I'll ever need the extra 1-2,000lbs of towing the lower gear provides. So I finally sat down and and did some math:

This assumes 150,000 highway miles over the life of the truck which if you keep the truck 10+ years is not unreasonable to see that many highway miles, I focused on this because lower gears(high numbers) usually get better mileage in the city anyway.

Diesel @ 3.60/gal
@28mpg; 150k miles / 28mpg = 5357 gallons x 3.60/gal = $19,285

@27mpg; 150k miles / 27mpg = 5555 gallons x 3.60/gal = $19,998

@26mpg; 150k miles / 26mpg = 5769 gallons x 3.80/gal = $20,768 Total Difference $1,483


Diesel at $3.80/Gal
@28mpg; 150k miles / 28mpg = 5357 gallons x 3.80/gal = $20,357

@27mpg; 150k miles / 27mpg = 5555 gallons x 3.80/gal = $21,111

@26mpg; 150k miles / 26mpg = 5769 gallons x 3.80/gal = $21,923 Total Difference $1,566


Diesel at $4.00/gal
@28mpg; 150k miles / 28mpg = 5357 gallons x 4.00/gal = $21,428

@27mpg; 150k miles / 27mpg = 5555 gallons x 4.00/gal = $22,220

@26mpg; 150k miles / 26mpg = 5769 gallons x 4.00/gal = $23,076 Total Difference $1,648



If someone had shown me that we'd be done. ~$1,500 over 150K miles/10 years is something I can live with. I've completely changed my stance from getting 3.55s to now getting 3.92s