Combine garlic, salt, pepper and rosemary. Press evenly onto all sides of roast.
Place rack in shallow roasting pan. Insert meat thermometer so bulb is centered in thickest part, not resting in fat. Do not add water or cover.
Roast approximately 18-22 minutes per pound for medium-rare to medium doneness. Remove roast when meat thermometer registers 135°F for medium-rare or 150°F for medium. Allow to rest for 10-15 minutes. (Temperature will continue to rise to 145°F for medium-rare and 160°F for medium.)
Meanwhile in small saucepan, combine jar of gravy, jelly and dry mustard. Cook over medium heat for 5 minutes or until bubbly, stirring occasionally.