So, I have been trying to cook grass fed beef for Italian Beef sandwiches. I have been using small chuck roasts (about 1.5 pounds), and also tried a sirloin roast. I try pot roast style in a dutch oven in the gas oven. Problem is: it cooks so fast. Too fast. I pull it out after an hour or so, and the Thermapen says it is already way past due (150+). The meat is gray throughout and already beginning to get tough. However, the fat/connective tissue has barely started to render. The meat does not seem to get that fall-apart tenderness. From the outside it looks rare, and from the inside it' well done. I have tried 275 degrees and 225. Thoughts please. Thanks.