Monitor your wheel bearings with ease by jacking up the front of your truck so your truck's wheels are off the ground at least 2 or 3 inches. Grab the tire at the top and try to rock it back and forth. If it does nothing, you are okay. If it wiggles a small amount, you may be able to just retighten the castle nut and roll with it for a little while longer. Should you find the wheel moves a lot, then you are guaranteed to be near failure.
Garage Tech Hints, Tips & Tricks - 101 Garage Tricks