J.R.
you got a lot of advice! :)
I finally made a good roast the other day after trying several times with it coming out tough.
I always put mine in frozen. Just a bit of salt, pepper, and garlic powder in it. A little water on the bottom (maybe a cup or so). Set it on low. Since it's frozen, it cooked from about 7 in the morning till around 4:30-5 in the evening and came out tender. good luck!
I realized by putting it on high and trying to cook it faster, the meat kept coming out tough.