chef,
Welcome. I'm assuming it was a brisket (maybe a 9 lb fish?) could be a large pork butt, but I'll guess brisket, so I moved it to the brisket forum.
First, after pulling it, how did it taste? Were you happy with the results, just not the time?
The shape can have an impact, thinner will cook quicker.
Have your checked your temp probe for accuracy? That's why I asked about the results. Key is results.
FInally, time is a rule of thumb, not an absolute. You WILL find some briskets cook quicker and some will take longer.
You didn't say what smoker you had.
Also the diff between 235 and 225 didn't make it cook that much quicker.
For the record, when I put my briskets in at 225 (which I don't anymore) I get closer to 1 to 1 1/4 per pd. But that's my smoker. The AQ and the electric CS tend to take longer.
Best advice, cook a bunch, keep notes and you'll get the times down for your smoker.