Let's look at and theorize the "big" and expensive failure issues you're likely to run into and what you could do to blunt them, BEFORE they occur:
1) Cam/lifter issues: This is probably the most likely BIG *expensive* issue you could run into. And it seems to be fairly prevalant. At 170k, you're kind of on borrowed time. Here if you wanted, I would suggest it would be a wise idea to consider being pro-active and get ahead of the problem ...if your goal is to avoid surprises. The root issue seems to be excess free-play on the lifter rollers. They're small and it's asking a lot for them to last 200k miles. And often they don't. With your truck's mileage, it's difficult to imagine they DON'T have wear. Therefore, if you wanted to reduce a big $urprise it would be a lot cheaper/easier to get on it now where it would be a lot easier/cheaper b/c you could just replace the lifters themselves (leave the cam) which is about half the work/cost.
2) Transmission: These seem to last quite a while. Have you replaced the fluid yet? Hopefully you have (like ...100k mi ago!!
). Beyond that, continue to do the service. I think the tranny is a run-to-fail item. Lot of guys make it to 200k and northward pretty easily. They're generall quite a bit cheaper than replacing the engine.
3) Electronic Power Steering: This is another expensive failure owners in your year-ish see. IDK what you can do to prevent problems. Maybe boost your savings account up a bit in case it does fail. Figure $2,500 to replace. And if it never does, celebrate.
4) ABS Module: Another failure-prone item in your year range. Again, it's pretty much going to be fix-on-fail with this item.
5) Misc: Wheel bearings/hubs (run-to-fail), WIN Module issues (You could clean the contacts proactively), Cooling issues (replace coolant), Bearing issues (Replace or lube idler pulleys), Starter/Alternator (run-to-fail).
So looking at the major failure points, the only one you can realistically pro-actively mitigate is the lifter issue. And that happens to be one of the most expensive failures, could result in needing a new engine. But relatively easy to swap in some new lifters. So, that's one you might want to target before it gets you.