i'm new here i do mostly highway driving and thinking of changing my stock 4:10 gears to 3:08s any thoughts

 

Even with the 4.0 i think 3.08's will make it a dog it will have zero acceleration. or towing capability. To improve economy i would consider 3.73 or 3.55. 3.73 seems to be ideal in these trucks it doesnt sacrifice to much acceleration or towing capacity but will provide a noticeable bump in economy. 3.55 will give you the most noticeable economy but will probably still have a serious impact on acceleration and towing abilities.

 

It would not tow or haul heavy loads well with 3.08 axle ratio
3.55 might be a better choice.

Overdrive on Rangers is a .75 ratio
3.08 would be 1,875rpms at 65mph
3.55 would be 2,150rpms at 65mph
4.10 would be 2,500rpms at 65mph

The lower ratio would certainly have better MPG at highway speeds but acceleration would be sluggish so you would have to accept that and keep your foot off the gas as you got up to highway speeds or you would defeat the purpose, lol.

4.10 = peppy but less impressive MPG at highway speeds, great for towing
3.08 = sluggish but great MPG at highway speeds, dismal for towing

 

That's way to low (numerically) for a ranger. It would use much more to get up to speed, defeating any gains you get at highway speeds.

Stick to 3:55 or 3:73

 

I'll vouch for 3.55's. I'm getting 20.5mpg in 50/50 mixed driving with a 4.0- auto in my ranger. It accelerates pretty hard, and seems to haul a load with no undue effort.
Also remember to turn your O/D off if your towing with taller gears.