Moving leaf springs

I was hoping someone could help me out with this. I was wheeling a couple of weeks ago and as i was driving up this hill and I thought I heard a pop. I was having front driveshaft problems so it ended my day early anyway, but somehow the right side (passenger side) of the axle moved back about an inch. It moved enough that when im driving and hit a bump my 35's would rub on the fender flares. I thought that maybe I had broke a centering pin and that caused them to move, but the pin is good, the shackles and everything look good, no broken springs or anything, so I dont know what else it could be. Could they just have gotten loose?
To be honest the PO installed the lift. Its a Rough Country 6.5" lift, and I have never bothered to check the tightness of the ubolts. Could there be something else im missing? Anyone have any ideas? The Jeep is for sale and im trying to sell it, but I cant sell someone a bum Jeep.

Thanks

There are only 5 bolts per side that hold a axle in place. 3 leaf spring/shackle bolts, 2 u bolts. I would guess the centering pin jumped a hole on the spring perch because the u bolts either broke or were loose. Maybe inverted shackle on one side? (pointing wrong way)

There's no way for the leaf packs to shift unless you've broken the centering pin or the u bolts weren't tight and it's jumped.

Take it apart, properly put it back together, don't worry about it.

If the centering pin is broken, its just a bolt right? Can I just replace it with the same size grade 8 bolt?

Yes and no.

The bolt that's supposed to be in there will have a round head. It's fine to replace it with a grade 8 bolt (that has a hex head), but you'll need to grind the hex portion to make it round so it fits in the hole on the axle. Not a big deal.

Can also get an allen head grade 8 bolt

I have never had a leaf spring apart before. So basically there is some type of perch on the axle itself. I have a 29 spline 8.25, and the bolt basically goes through it with the head fitting in or on the underside... Is that what im hearing you guys say?
Sorry for the newb question. This is my first XJ.

The "centering pin" essentially looks like an allen head cap screw but without the hex recess in it. I have used allen heads in the past in a pinch to replace a busted centering pin. It just fits in a hole in the spring perch on the axle, as well as holds the leaf spring together (so you'll want to clamp the leaves with C-clamps before removing the U-bolts if you suspect the head is sheared off the centering pin, otherwise you'll be in for a world of badness.)

I was hoping that I had some pics of me swapping the leaf springs on my old Studebaker to illustrate, but no such luck

You might wanna check all your bushing as well. Especially frame side on the leaf spring. I'm not sure if that would cause your issue but it wouldn't hurt to check.