How long do i cook a 2 and half pound chuck tender roast in crock pot?its not round its more flat.?

You can put it on high for 4 hours or low for 6 to 8. And, periodically check it. Might only be 2 1/2 pds but crock pot doesnt get as hot as an oven. Also, when cooking in Crock Pot do not constantly life lid, as you loose the heat each time lifted.