So, after grilling a half picnic roast of pork (about 5lbs) for around 12 hours at about 200 - 250 (F) I found half of the final product to be tender and half tough. I sprinkled it with salt the night before, and then put on a dry rub over a splash of water a few minutes before it went onto the grill. I had planned to keep it on the grill (propane) until the internal temperature to had risen to about 200. 10 hours into the cook I kicked the temp up to about 300. The internal temp was about 192 when I took it off.
In the end, a large part of the roast pulled apart nicely like I expected, but some sections would not and seemed to be very dry. Only about half of the final pulled pork was edible.
I was monitoring the temperature with a dual probe thermometer, one probe in the meat and one in the nearby grill air. Unfortunately due to lax attention and some shifting weather that day, the grill temp did drop below 200 several times during the day, once for over an hour (I know thanks to the fancy history chart in my thermometer). The internal temp stalled at about 140 for over an hour but for the most part it was progressing nicely.
Did I overcook this by letting the grill run too cool for too long? Or was it from spiking the temp to 300 at the end?