I have a 2001 w 170K. Here’s my recommendation - you have to change all the fluids (sounds like you have) plus make sure you have good brakes. And it’s cheap insurance to have relatively new battery, less than 36 months. After this, tires are a big purchase; $600-$1200 but it you need them you gotta’ get them. New $600 tires are a world better/safer than bald Michelins.
And a splurge, those old paper cone speakers, yep - for $350 you can have 4 new door speakers and an 8” subwoofer (4” max depth). This will make driving the car much more enjoyable and it’s an easy DIY (I used Polk and have a thread on it).
After that, you have to pace yourself because No matter how much you put into it, it’s really difficult to make these GMT800 SUVs worth more than $4000- 6000. I dealer recently offered me $965 for mine on trade for DW’s new Acura, and told me the same - no matter what I’d done to it over the years really didn’t matter. I turned that offer down (of course) but was interesting discussion. So I keep myself on an annual budget of $1000-3000. I’ve got my projects mapped out. I’d like to replace coils, plugs and wires, rear shocks, and O2 sensors … but I’ve already completed this year’s projects (water pump, radiator and front shocks). So ignition, O2 sensors and rear shocks gonna’ have to wait. If you hold yourself to an annual budget - you’ll have a really good driver for $100-200 bucks a month that you don’t have to spend until you decide to spend it. That’s the beauty of these trucks. At any given time you can drop a few grand in and fell good that you’ll eventually be able to drive your money’s worth out of it …. But you can probably hold off spending anything once you get a few basics taken care of. This is the approach that works for me. Three years ago I wanted to out a new head unit in , but I had to get a new AC instead… so I put it off. Hope my input helps you manage your truck. Enjoy the ride and see you out there!