I recently replaced my hub assemblies. There's different ways to try to tell which one is bad, more noise turning one way than another, jacking up the truck, putting your hand on the spring, spinning the tire and see which one "feels" bad. But, the bottom line is, if one is going, chances are the other is right behind. In my case, they sounded really bad driving, but it was pretty hard to tell for sure which one it was. So, I opted to do both. They ran 177 each, but with a promo code, got them for 120 and change each. Also, since you have to pull the brakes completely off, if they're not brand new, it is worth it to replace them at the same time. It really isn't a hard job, just follow instructions found on this forum.
When I did get the bearings off, they didn't feel too bad. It is hard to believe that they had made so much noise. But, it is now like a new truck!
Good luck.