You can overcook stew meat in a slow cooker, but the slow cooker significantly reduces these odds due to the low and slow cooking method and the amount of liquid. Keep in mind that the cooking time can vary depending on your slow cooker, so check early if your crockpot tends to run on the hotter side. Chuck roast is fairly forgiving thanks to its marbling, so if you go over on time, all is certainly not lost. Your vegetables may be a little mushy, but your stew should still have great flavor.