Making gravy in a crock pot is not easy; it rarely ends well. It just doesn't get hot enough for most flour methods. So we will make gravy "with" a crockpot meal but not "in" the crockpot. You can make a roux, add it to the crockpot, and turn the heat up with a fair amount of success. That takes time. But moving the fluid out of the crock pot to a stovetop pan works much better and is more reliable. See How To Make Gravy at Home for details on gravy making.