I just got a new 18.5" and made a small brisket (5-6 lbs.) for the first time using HH method. Pulled at 170 after cooking for 1.5 hours at 375 or so. Double-foiled and returned for 1.5 hours. Tested for doneness. Wasn't butter soft. Put in a cooler wrapped in a towel for 2 hours. Checked for doneness but still a little tough. Great bark and taste though. Why wasn't it like butter? I've cooked big packers on the old 18" in the same way with much better success. Did I overcook the smaller piece of meat??