It started and burned well enough. And the lumps were all regular
shapes and similar size, and the fire was easier to keep. I used
hickory wood chunks for smoke, and the prime rib came out OK, but not
as flavorful as when I use hickory or mesquite lump.

The problem with the mesquite lump I've been using (Lazzari's or El
Mexicano brands) has been that to muchof the bag consists of
half-dollar or smaller sized chips; only a few larger pieces.