In a bowl, combine 1/2 teaspoon chili powder, salt and garlic salt; rub over roast. Place roast fat side up on rack in shallow roasting pan. Bake, uncovered, at 350 for 1-1/2 hours.
In a sauce pan, combine the jelly, ketchup, vinegar, and remaining chili powder. Bring to a boil; cook and stir until the jelly i smelted and mixture is smooth. Reduce heat; simmer, uncovered, for 2 minutes.
Brush 1/4 cup jelly mixture over roast. Bake 10-15 minutes longer or until a meat thermometer reads 160 degrees F. Remove roast to a serving platter; let stand for 10-15 minutes. Skim fat from pan drippings. Stir in remaining jelly mixture; heat through. Slice roast and serve with sauce.