What temperature did you cook it to? Usually dry and/or tough brisket is under cooked. Buy a good remote read electric thermometer. Cook the brisket to 195 degrees internal temp, and then probe your brisket with a skewer. When the skewer goes into the brisket with the feeling that it warm butter, it is done. The brisket will actually jiggle like it jello. Wrap the brisket, and place it in a warm ice chest for 2 to 4 hours before slicing.