Dana rear axle
 

What is the Dana number for a Grand Cherokee Orvis A 1998, and where can I find it?

It's either a D35 with the 4.0 or a D44a with the V8. The D44a should not be confused with the D44. It's bigger and made with an aluminum center section. The D44 was not used in jeeps.

Good point. The D44a was used in the grands. The D44 was actually used in early XJ models but are hard to come by

I know that people feel that certain axles are better than others (D30 Vs D44 for example) and that is justifiable, but it seems that even the "weaker" axles can be upgraded (up to a certain point of course) that would make them as reliable as other higher rated axles. would you agree?

Yes and no. The D30 and D35 are medium duty axles designed for passenger cars and light trucks. They don't take well to hard off-road bashing. The D44a case will stretch enough under hard usage to change the gear tooth lash and cause the gears to spaul and the bearings to fail. A truss installed on the D44a will keep the axle tubes straight, but won't do much for keeping the case from spreading.

I'm sort of biased, but the most rugged differential in my experience is the GM 12-bolt truck rear axle. My 67 Special High Performance SS Camaro had one in it (the truck one) and I never destroyed it while drag racing, and my Chevy trucks got beat pretty good also. I think those are 8.875" ring gear.

Of course there's the Ford lineup.

the dana 35 in a xj which is lighter breaks on 33 inch tall tires,The dana44a can stand up to 37s if you truss it and skid plate it.Or you can swap in it a ford explorer 8.8 but that takes some welding to do it.The front dana 30 if you beef it up it can handle 35s no problem,And anything bigger then a 35 inch tire you need to swap in bigger axles.