200K miles? That actually seems low. I've heard of these going 300k + before needing major work. I had a friend with a 2002 1500 - who had something like 350k miles on his.
Everybody thinks wheels and tires when they think of "mods" , but I think there's a few things that you can do to these trucks that make them nicer to drive and last longer , but they still stay nominally "stock".
I used to have a 2003 2500 Suburban , ended up selling it because it was getting badly enough rusted that I just didn't want to deal with it any more.
Picked up a 2010 Yukon 2500 after that and made a few mods to make it a little more reliable / easy to deal with on a daily basis.
I noticed a few times when driving in REALLY hot weather and then getting stuck in traffic - that the trans temp was headed up to the danger zone. I plan to put a bigger cooler on the truck , but in the meantime when I did the transmission service I replace the pan with a deep pan from PML. It DOES work - I' say it brings the trans temp down 15 degrees or so on the average.
I also noticed that when the truck got up to about 105,000 miles it was really wandering severely on the highway. I planned on replacing wheels and tires because it needed tires and I wanted to go to 20" wheel so I could accomodate larger brakes. So shortly after replacing the wheels and tires - I rebuilt the entire front suspension and adjusted the steering box. That made a big difference - the truck tracks really nice on the highway now. I didn't go with just factory stuff though - I went with an upgraded upper control arm from Cognito, a Bilstein damper, adjustable shocks from Fox, upgrade Idler arm with the weld in brace, upgraded pitman arm, and upgraded tie rods.
Doing all that made the front end nice and tight.
Later I added a set of the big Wilwood brakes on the front (still intend to do the rear).
Doing all of that stuff has made the truck a lot more "driveable" I think. I even drove it in rush hour traffic - where the better braking came in handy a few times.
The chassis on the GMT800 and GMT900 3/4 ton SUVs is pretty much the same. So the same upgraded parts I put on my truck would also work on the earlier trucks as well.
