In a small bowl, whisk together the cranberry sauce, lemon juice, mustard & brown sugar, then pour 1/3 of the mixture in the bottom of a 5-quart crock pot.
Place tenderloins on top of the sauce, then pour the remaining sauce over the meat.
Cover & cook on high for 1 hour, then turn the temperature to low & cook another 4 to 6 hours or until meat is tender.
Allow meat to stand 10 minutes before slicing & serving.