Pork Shoulder Blade Roast (AKA Boston Butt), and a few other names are all part and parcel the same cut of pork...The top portion of a pork shoulder.
The "Picnic Half" is the lower portion of a pork shoulder...The Boston Butt, and Picnic together make up the pork shoulder....Both are excellent using the various slow, low temperature, long cooking methods....
I agree with Andy...You may have not cooked the roast to a pullable stage...Around 180* the meat is sliceable....185* Sliceable, and somewhat pullable...190*- 195* The meat is very pullable. Like Andy suggested, a thermometer would prove very valuable.
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