Just drive.
With these trucks it’s simple… you shouldn’t hear anything at all and everything should work as intended. It truly is not like a standard car you have driven in the past. People may overuse this statement but these trucks are built with a 25 year service life in mind. At 21 years and 218k miles, i can vouch for that.
Now, that doesn’t mean you can completely ignore preventive maintenance; and you’ll find through the forum that a lot of issues can be avoided with preventive maintenance in the forefront. The faq’s get into this some detail, but I’ll shoot out some that I think will help you baseline.
timing belt/water pump. If you have no record of that being done, do it. One of the few items that can kill this engine.
Heater t’s - do them. More likely to fail than a water pump/timing belt, simple to change.
Spark plugs - they can come loose and cause some issues if not torqued adequately
Change your oil - in the differentials, gear box, transfer case.
Some not so maintenance items that have become maintenance items:
The starter tends to go out - I’m on the third (more like signs of giving up but never left me stranded)
Alternator - on my second, didn’t leave me stranded just stated making noise and reporting low voltage levels.
If you don’t have any clear signs (leaking, unusual noise), it’s likely none of these are imminent failures but something you want to take care of in the future.
if this is a NE truck from the rust belt you may encounter other issues so I’ll let others chip in but at 139k, you should be in good shape!