Stock Gear Swap

I have a 91 XJ with a 4.0/AX-15 and 3.07's turning 31's. Since I've done the 31's I've wanted lower gearing than the 3.07's. I cant tow anything and fuel mileage sucks. Since all the aw4 equipped XJ's either have 3.55's or 3.73's, I was wondering how hard it would be to swap in a set of 3.73's from the salvage yard. What all would be involved for both axles?

Thanks

Off your topic a little but I have a 92 with ax15 and 3:73's. All I can say is if your going to stay with the 31's go to 4:10's. My mileage is about 12-14 and constanly have to down shift from 5th if I need any kind of get up and go. Even on flat land. Dont know for sure how to do the install (had mine done by another member) but if you go with 4:10's you will need diffrent carriers, from what I understand.

I agree with you guys that 31s and 3.07s suck, but my mileage is great. I get 17-18 mpg around town, and 21 mpg on the highway. I never use fifth gear. If I never took my Jeep off-road, I don't know that it'd be worth the expense to put in lower gears.

I get 15 MPG and its killing me. I towed a trailer that couldnt have weighed more than 750 pounds and 55 was my top speed. I've given up on using overdrive at all

Yes, it'd be worth regearing. Your mileage isn't great, it's average at best. I get ~16 commuting and ~18-19 on the highway with 33s and 4.56 gears behind an AX15. I got 22-24 mpg on the highway when it was stock.

For the easy regear, you'll swap the entire axle assembly, not just the gears. If you just swap the gears, you'll need to do a full gear setup.

I was hoping It wouldnt come to that. Are there any ways to tell if used axles are any good?