Thanks for pictures and the report. Looks good. As far as advice, I've only done a couple of boston butts, so I'm not sure if I'd be much help. Not sure what kind of PB you have, but I'm assuming having 3 BB's on there at the same time probably kept your temp down around 170 using smoke mode, which is why it took so long. I'm wondering if it would be better to set it at 200 instead and add a smoke tube, or adjust your P setting so that it feeds a little more often to maintain a slightly higher temperature.
When I did mine, my smoke setting kept it around 190-200 degrees and I left it there for 4-5 hours. Then I bumped it to 225 for another 4 hours. I then wrapped it in foil and set it at 300 degrees until I reached an IT of 200 (about 2 hours), then let it rest in the foil for about an hour. Mine was pretty good, but I feel like I could have left it on the grill wrapped in foil for just a little bit longer. It pulled pretty well, but was a bit tough to tear in some parts. But it tasted great.
I think my rub had a little sugar in it which also helped the bark color. When I pulled, I had plenty of juice in the meat and foil to keep things moist.