hey, so I'm new to the fords and I had a few questions that I was hoping to get answered.

I have a 1980 F-350 with a 400 and a 4 speed std transmission. It has the 4.10 gr in the back.

So the problem I am currently trying to fix is fuel economy and more driving pleasure. I dont use the truck for heavy hauling or offroading.

-Is the a 3.73 diff that is interchangeable? And if so what year/model/engine size.

-How much would a 3.73 diff change the fuel consumption and would I drastically see a difference in first gear..... or should I say will I actually get to use a first gear?!

-Is there a 5speed transmission that is interchangeable? (year n wtv) and do I need to change to the hydraulic clutch or are there any options with the mechanical clutch assembly that I already have?!

thanks