I recommend using apricot preserves in the pork tenderloin glaze. Apricot preserves are thicker than apricot jam, which is why it works better in this recipe. However, if you only have apricot jam on hand you can definitely still use it. However, at the end of the cooker time you might want to transfer the juices from the slow cooker to a saucepan, add 1 tablespoon of water and 1 tablespoon of cornstarch, and then simmer over medium-high heat to thicken the glaze.