My beef stew recipe doesn't call for any thickener (cornstarch, tapioca or even browning the beef beforehand).
Actually I have the opposite "problem." I need to make a gravy (I make the packet AuJus) to add to it to make it more like stew (this is really really hearty). It does have tomato paste in it so that could be what helps it stay thick. (I got this from the Penzey's spice catalog years ago.) It's ridiculously simple but so very very good. I cook it in a covered stoneware dish in the oven but I imagine it would work in slow cooker too.
1 1/2 pounds stew meet, cubed
6 cups peeled cubed potatoes (about 4 large or small red potatoes unpeeled)
12 small whole pearl onions or 2 medium onions cut into chunks
4 cups carrots cut into 3” rounds (5-6 medium carrots)
2 cups celery cut into chunks (2 large stalks)
1 (15 ounce) can petite diced tomatoes or 2 (8 ounce) cans tomato sauce
1-2 teaspoons salt
1/2 – 1 teaspoon freshly ground pepper
1-2 teaspoons Oregano
1/4 – 1/2 teaspoon garlic powder
Cover and bake at 250 for 4 - 5 hours.