Rub prime rib with garlic salt, seasoned salt, and pepper. Place roast, fat side up in shallow pan. Insert meat thermometer in center of meat and roast at 300°F. Allow 20 minutes per pound for rare, add about 30 minutes longer for medium and 3/4 of an hour for well done, but be sure to watch your thermometer as roasts differ in shape and size, and all ovens vary in intensity.
Remove from oven and let roast stand,covered, a few minutes before carving.
Add a little water to drippings for an au jus.
Add 1 cup warm water mixed with some flour to drippings and thicken over medium heat to make a gravy.