will a two speed rear end improve my mpg?

 

No. According to some of your posts, you have an F350. You are looking at F500 or F600 2 or 2 1/2 ton for a two speed axle. The axles from those trucks will not go under your 1 ton. Way too big and heavy.

 

so its probably not a project worth undertaking ;moving springs building a driveshaft bla,blah just to see the rear end i got was out of a 600 thanks

 

I edited my reply based on looking up your posts regarding what truck you have. I remember a guy 30 years ago running an F350 haveing the same problem. He had a 4 speed and was running the whee out of it on the highway.

You can look into:

-taller diff gears
-od tranny
-bolt on od for your tranny
-taller tires

Costs and limits and of course, your mileage, may vary.