When driving at low speed, 20 to 30 mph, I can hear what sounds like a knot on the tire. I raised rear end off the ground, put it in drive, and just let it idle while wheels turned. I could distinctively hear a clumping sound coming from behind right wheel. clump clump clump clump. Is this a bearing?

 

Yep. Probably a side bearing for the carrier

 

Lift the truck with a jack and put it on stands. Put it in gear and let it run on the stands. Use a stethoscope to "Zero in " on where the noise is coming from. That should narrow it down quickly

 

you might take the tire off and examine the brake area for problems, If you have a disc with emergency brake inside, that is right next to the bearing. Might pull disc, look at brake shoes, retest for noise with tire off.