This. Just keep driving and being attentive to the maintenance, as you should. if you have nothing wrong now, then just keep note of any feel/sounds/CELs that arise.
People tend to forget about the trannies and diffs, so a fluid change would probably be appreciated. Rad flush could probably help - and an external tranny cooler would eliminate any chance of pink milkshakes. Some people flush their power steering but I never have.
New fuel filters never hurt and are usually forgotten about.
You could replace your ball joints with some fresh ones, as they're probably gonna be the original set, that is if you have the money (lower is more crucial and cheaper/easier to replace than upper)
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Y2K Highlander
Millennium Silver 3.4L auto @ 320k and climbing
Toytecs + 5100s / 7.5 wrap + OME spacers + Tokicos / JBA UCAs / Anonymous Fab. LBJs / Total Chaos Gussets / EimKeith PCK + LCAR / Extended Bump Stops; Brake Lines; Rear Diff Breather / True North Fab. Hybrid Bumper / CBI Hybrid Bumper + Tire Carrier / 4xInnovations Hybrid Sliders / Opt Offroad Trailing Arms / Lil Skip Gas Skid / BudBuilt Front Skid / ARB Rear Locker