In a microwave-safe bowl, combine the jelly and horseradish. Microwave on high for 1 minute or until jelly is melted; stir until smooth.
Place the tenderloins on a rack in a shallow roasting pan. Brush with half of the jelly mixture. Bake, uncovered, at 425° for 20 minutes. Turn the meat over; brush with the remaining jelly mixture. Bake 10 minutes longer or until a thermometer reads 160°. Remove the meat and keep warm.
Add broth and grape juice to roasting pan; stir to loosen browned bits. Transfer to a saucepan. Cook over medium-high heat until liquid is reduced to 1/2 cup, about 5 minutes. Strain sauce; add salt and pepper. Slice pork; serve with sauce.