A 3 pound chuck should have cooked faster than what you did, but, 225F is slower than I generally cook. I am sure you need to check the probes and make sure they register temps properly. Fill a glass with ice, and then add water, stir as if making a cocktail. Put the probes into the water for 30 seconds and it should read 32F or close.
I'm feeling bearish, and I'm packing a Wusthof Grand Brisket slicer from MABA
"perhaps...but then again...maybe not..."