Here's the other three pictures.  I'd recommend lifting the front end of your truck off the ground, check for any excessive tire wobble which could indicate bad wheel bearings, a loose spindle nut, or like you mentioned, bad knuckle bearings.  During the disassembly process, you can progressively check it out but I wouldn't necessarily stop.  There is a chance you have multiple contributors to make a problem like you describe.

If you've never done it, the knuckle rebuild kit from Marlin certainly can't hurt.  I did mine not too long back when I was dropping third members and it wasn't very difficult.  Besides, it's a good chance to take a look at the Birfields, clean the hubs, replace the inner axle seal, and grease everything back up.  While you're at it, you should slap a Marlin High-Steer in it.  I gotta do it to mine.  Only takes $$$.

If you do order parts from Marlin, he's got a fish scale that really does the trick for tightening and checking your spindle nut torque.