Too small a butt. If you have a butcher shop try asking for a 10+ lb one.
Figure the meat is done getting smoke at 3 hours into or 140 internal temp. Its just the nature of the "can" we use.
Heck, after 5 or 6 hours you might as well put in the oven or a crock pot!
As for smoke taste? Maybe try a tad more wood or a thicker tasting wood. Each has their own preference.