Okay, now that I am on the right page..............
I wouldn't tow another SUV with the X. Some may say it is okay, but I wouldn't. Something smaller like a YJ would be okay, but no XJ.
Remember, when you hear Jeepers talk about D30s, they may be referring to two different axles. A HP, RC D30, like in your XJ, is a stronger axle than a LP D30, such as in a TJ (estimate is about 30% stronger). It is a common swap for them to go from LPs to HPs.
As Hokie mentioned earlier, most Jeepers recommend alloy axle shafts if running around 35" tires. I don't believe the XJ uses the two-piece passenger shaft, so that is good if you choose to stick with stock shafts (I may be wrong about that). Most agree to not go to a gear ratio lower than 4.56, some actually say 4.10. The R&P in a D30 is just tiny.
The good thing about the Jeep is the aftermarket is FULL of lift kits for whatever you want to do. I would do the research into exactly want you want, then keep your eye on eBay. There are more Jeep kits on there than you could shake a stick at! Coils, pitman arms, trac bars, whatever...........it is all there, and cheap. Keep an eye on the Jeep Forum classifieds also. A lot of guys that have swapped up to beefier axles sell off their older stuff real cheap.
When researching lift kits, axle swaps, and stuff like that, I have found the best way of doing it is this. Look through every website you can possibly find until you come across a rig like yours with the strength, manners, and capabilities that you would like to see in your truck. Then just copy the hell out of them!
There is no reason to spend, the time, effort, and money to try to invent a new way of doing it. Take as much free advice as you can from others that have been where you are now.
okay, I am rambling, enough for now.................
ps: I do still have a set of Warn D30 alloy shafts available. I am not sure of the exact measurements of the XJ axles, so I am not sure if you can use them. But, if you can determine that YJ and XJ shafts are the same, I got them.