Combine first 6 ingredients in a shallow dish or large heavy-duty zip-top plastic bag. Cut deep slits in roast using a paring knife; add roast to marinade. Cover or seal, and chill 8 hours, turning occasionally.
Soak wood chunks in water 1 hour.
Prepare charcoal fire in smoker; let burn 15 to 20 minutes.
Drain wood chunks, and place on coals. Place water pan in smoker; add water to depth of fill line. Place roast in center of lower food rack.
Cook, covered, 6 to 8 hours or until a meat thermometer inserted into thickest portion registers 165°, adding additional water, if necessary. Remove from smoker; cool slightly. Chop or shred; serve with barbecue sauce.