Everything!
If it is found under the front end of a cummins dodge and it moves, it doesn't last. The popular upgrade from Y-style to T-style steering linkage is definitely worth doing when your current front steering gives out, imo. There are lots of threads here covering it. The most popular replacement parts are from Moog. Such as ball joints and t-steering linkage.
Mark, Cumminspower98 here on TDR, has a nicely detailed webpage of that mod and many other very practical ones. Here ya go:
My Ram His website is chock-full of great ideas and details.
I copied his very clever greaseable hub mod when I rebuilt my frontend, too. Other worthy upgrades would have to include a 3rd generation trackbar (I opted for the adjustable one). Adjustable poly-bushed control arms. Definitely the steering box/steering shaft support. You'll find it all on Mark's page and here.
The parking brake mod is one I came up with and it cures the very unreliable '96 p-brake and also makes it function like a normal p-brake by staying down as well as set. You should be able to find it with a search.
The list of upgrades that
can be done is very long indeed. There is also the list that 'should be done' to any '96 you plan to keep and drive much. Very little of it involves doing anything to the Cummins aside from the kdp and fuel lines, etc. The engine is not the problem generally. But do not skimp on the steering, suspension, and brakes; all of which leave much to be desired. All the reliable diesel power in the world is worthless if you cannot get it to the ground and keep the truck safely between the fenceposts. And the term "Death Wobble" is very much a "dodge thing". You will never mistake it for anything else short of a magnitude 7 earthquake or category 5 tornado.