At 275F, you are looking at not enough time, I usually end up with 7 to 8 hours at that temperature, all is not lost though. Cook for another hour or so, until the butt is nice and mahogany, then put in a pan, add some apple juice, foil securely and put the spurs to it, 325F, even 350F, and let it rip. You will be done about 3 hours after you put it in the pan, you can judge by the bone. Cutting it up into 2-3 chunks will aid in that process.
I'm feeling bearish, and I'm packing a Wusthof Grand Brisket slicer from MABA
Whip It Off, Chambers!
"perhaps...but then again...maybe not..."