For beef dip or a French dip sandwich, I use a cheaper cut of roast that I would use for pot roast, a cross-rib roast, or a chuck roast, for example. I haven't cared for the results I've had with my crock pot either.
I finally found a pot roast recipe on the net that was perfect. Rather than following the times indicated for cooking, I roast it until it's medium well and remove it to a platter. Don't overcook or it will be dry. I take it out when the meat thermometer reads 160-165 degrees F. I also brown the onion with the meat.
The recipe from the net:
"2 teaspoons olive oil
4 pounds boneless chuck roast
1 onion, chopped
2 cloves garlic, minced
2 bay leaves
1 teaspoon salt
1/2 teaspoon freshly ground black pepper
Preheat oven to 325 degrees F (165 degrees C).
Heat a heavy Dutch oven on top of the stove over medium high heat. Add oil, and sear meat in the center of the pan for 4 minutes. Turn meat over with tongs; sear all sides for 3 to 4 minutes on each side. Remove meat from pan. Arrange onion, garlic, and 1 bay leaf in the bottom of the pan, and sprinkle with salt and pepper. Return meat to pan, place remaining bay leaf on top of meat, and cover. Roast in the oven for 30 minutes at 325 degrees F (165 degrees C). Reduce the heat to 300 degrees F (150 degrees C), and cook for 1 1/2 hours."
The roast generates lots of "juice" which I'll then combine with a "dip".