[hayden55]

I'd probably get low rolling resistance car tires first before I got a new axle. The axle will help but its not going to be an absolute ton. Your ranger is specced out to weigh 3100 pounds. I would get you a set of either 195-65/15 Michelin Energy Saver a/s or some 195-65/15 Bridgestone Ep422. Your car weighs about the same as my prius (3050), and the load ratings work and I can still tow my boat and what not. My mpgs went from struggling to get 51 in spring weather to averaging 63 mpg (both were max effort). Key was I had 7 year old non low rolling resistance tires in the correct size but the actual tread width was also 6.2" vs 5.6" of my 185-65/15 ep422.
The key with the axle is finding something that is already assembled so its cheap to swap in. Ford axles are a dime a dozen and easy to find. I know im a mustang guy/ ford truck guy as well. I'd say go as low as you can on the gear ratios and you will more than likely gain a ton of mpgs from 55-65 but only a marginal amount at 70 mph. (3.08 3.15 3.33)