I've made pastrami from store bought corned beef a couple times and every time it comes out really tough. What am I doing wrong? Or is it simply from the product I'm using? My method is as follows. Buy the corned beef (or defrost one from last year) and then cover in mustard and my rub. I smoke low at 200-225 until it reaches an IT of 190-200. No matter how might up I got with the temp it just never reaches toothpick tenderness. Is it from cheap briskets or am I doing something wrong? My last pastrami took about 8 hours and was real small, only a pound or two.