Yesterday, I smoked a trimmed brisket (flat) on a Brinkmann Trailmaster Vertical smoker using the pan method in Jeff's book. At 5.25 pounds I expected it to be done in 8 hours. I used 3/4 lump and 1/4 briquettes and occasionally added Mesquite. I inserted remote meat thermometer at 3.5 hours and flipped the meat. After 7 hours total time, CC was still running at 235-250 but the meat was only 151 (plateaued for almost 2 hours) so due to time constraints placed it on my old Brinkman Horizontal to finish. Paid the price for doing this as the meat was tough. Anyone have any thoughts on the meat temp plateau?