Sprinkle salt and pepper liberally on tenderloin and brown in frypan with cooking spray, frying for 4-5 minutes per side.
Add half apple cider/juice to crock pot, then add one sprig rosemary. Place tenderloin in slow cooker, then remaining rosemary. Cover with cherries.
Cover with lid and cook on low for 5-6 hours.
Remove roast from slow cooker, wrapping in foil to keep warm.
Pour sauce into saucepan, removing cherries and rosemary (use a strainer). Add ¾ cup cider/juice and bring to boil. In a small bowl, combine last ¼ cup cider/juice with cornstarch and slowly add to saucepan. Boil for 1-2 minutes until sauce is thickened. Serve sauce over pork.