The cooking temp was pretty low throughout most of the smoke (keeping it somewhere between 225 - 250). Also, because I cook on a Weber 22 1/2" kettle, I had to lift the lid about every 45 minutes or so to add a few briquets, rotate the turkey, and add a pouch of smoking chips (only to 140), which I'm sure extended the cooking time considerably. The only high heat was during the initial hour or so, because I wanted the skin to be a little more crisp and edible.
In retrospect, I would have probably pulled the bird an hour or so earlier, especially since I realized the variance in cooking temperature between the grill grate and the lid (around 50 degrees), which did result in a slightly drier top half of the breast - but even that was still moist and very tender. Now the lower half of the breast, wing, thigh, drumstick, and the back of the turkey were very moist and juicy.
Second, I was using new meat thermometers and a little unsure of their accuracy (*note to self: never use new meat thermometers when cooking a special holiday meal, leads to indecisiveness. Kind of like I would not use a new and untried putter for a golf tournament).
The last variable that might have increased the cooking time was the cool temps and heavy marine layer here in the Bay Area when I cooked the turkey. I've noticed when I cook during the cool and "heavier" air conditions of the fall and winter here cooking times seem to increase somewhat. I may be mistaken on this, but it seems to have some influence.
Yesterday had a little leftover, and the meat was even more moist and tender after spending the time marinating in its juices.
Trust me, I was sweating bullets at the long smoke too, I was so afraid that when I cut into the meat it would be like sawing into leather, but it was quite the opposite, there was quite a bit of fluid that came out - much to my relief and surprise.