I agree, not cooked long enough and possibly not rested long enough. Dd you let it rest at least an hour before slicing? If not, the juices didn't redistribute and most likely ended up on your cutting board. Cook it til probe tender, as explained above, foil, and rest. I rest mine by wrapping in foil, a couple of towels, and placing in a clean cooler, or empty oven.
IMBAS Certified MOINK Ball maker and IMBAS Sgt. At Arms.
And now, brethren, I commend you to God, and to the word of his grace, which is able to build you up, and to give you an inheritance among all them which are sanctified. [Acts 20:32 KJV]