No, not better mileage, but not really much worse in reality. Some folks who have swapped from 3.73 to the 4.30s have seen the same or even better mileage in city driving as the deeper gears get the big wagon moving easier, some have seen about 1 or less MPG on pure highway driving. On my EX when it had the factory 3.73 gears it would get 14-ish on my 50/50 city/highway commuter mix with a best ever tank at 15.5 MPG while touring coastal Maine on a very hot day. Now with a 4” lift, 4.88 gears, 35” X12.8” tires, Banks headers and running the 89 octane performance tune from 5Star it still gets 14.5 MPG with the cruise set at 65 MPH on an all highway trip. My effective ratio between the deeper gears and taller tires is 4.39, so pretty close to what you have with stock sized tires. And in my case the lift and bigger tires are working to some degree against the mileage.
With this large and heavy of a gas powered vehicle it’s really important to treat the go pedal gently if getting any kind of decent mileage is in your goals, in all of the MPG threads that I’ve read here it seems that I do pretty good with higher than average results, I credit driving my ‘94 Geo Metro XFi as my good weather daily, it typically gets tanks in the lower 60 MPG range, paying attention to driving habits pays off in better MPG results.

 

Thank you for all the replies! I am learning a whole lot! I've been ordering some parts trying to get ready for the job, but there is one thing I am having trouble with. Do you guys know where to find the factory sized ubolts? I have found it's difficult to find the right sizes because I keep finding ones that are too long.

 

If the U-bolts are to long, you can fix that with one of these (or one of it's powered counterparts) easily enough.

 

Pmf
https://www.pmfsuspension.com/Ford-1...olts_p_43.html

or your local spring shop