Mark,
Let me make a few observations here.
First, and this is not to say that Stuart is wrong or that I am right, but it always makes me stop and think as to why you would sear a roast before putting it into a smoker. Now I realize this is one big hunk of meat but placing the roast in the smoker, I want it to pick up some smoke penetration. It won't get much but to me it will get even less if it is seared first.
Second, I can understand Tom's suggestion to rest the uncooked roast on the counter for a while before cooking. A piece of meat that size will bog(for lack of a better term) down some smokers. IMO, it is more difficult to go from 35* up to 90* than from 90* up to 125*. It takes momentum to get it going. Such is the suggestion to let it warm up some. If you are not comfortable with four hours, make it 3, 2, or 1. But anything less than at least an hour won't do much for you anyway.
Like Qnorth says, do some other kind of roast. I like to make top sirloin roasts.
But most important, keep doing it! Practice makes perfect.