You're doing it wrong.
First off, I would cook a chuck at 275F minimum. They take too long other wise. I prefer a simpler rub, but, the Plowboy's Bovine Bold is an excellent rub, I find it a tad salty, but, it works great (and I am on a lower salt diet). That was not the problem.
My process (if smoke ring matters) is to start the cook off when the UDS or kettle hits 225F, then keep the vents open until it hits 275F, shut the bottom vents to where I think it will coast up to around 300F and hold there. Run the cook time from there. A 3 pound chuck, I am looking at 4 hours, no peeky. At four hours, I will probe and see what I have. If it is tight, then 2 more hours at 300F, if it is close, then 30 minutes and check again. At 300F, you should reach the pulling stage in 4 to 6 hours. Never pull it before it probes tender, chuckies need to be cooked to completion either straight through, or panned, they have to be pulling tender on the pit.