You undercooked that chuck. And you can go a lot hotter than 225F and get great results. Now, back to the chuckie, it is undercooked because:
1. It is dry
2. It is really well consolidated
3. It slices perfectly
I have found that given equal weights, chucks often take longer than briskets. They also respond much better to wrapping and liquids than briskets. When you look at a dry piece of meat off the smoker, if it slices very cleanly and is dry, you can believe it is undercooked. If it is dry and the edges crumble, or the grain just shreds, then you are looking at overcooked meat.
I'm feeling bearish, and I'm packing a Wusthof Grand Brisket slicer from MABA
"perhaps...but then again...maybe not..."