Combine all of the ingredients for the Garlic Herb Marinade and pour over the roast. Place roast in the fridge to marinate for 8-12 hours before grilling. Remove from fridge an hour before grilling.
Roast on Bull Grill using indirect heat at medium-high (approximately 500 degrees) for 10 minutes to develop a crust. Lower temp to medium (approximately 350 degrees) and loosely tent with aluminum to prevent the crust from burning. Cook until the desired doneness.
Remove from heat and place in a warm area or loosely covered with aluminum foil. Rest for 20-30 minutes before slicing.
To make Garlic Horseradish Sauce combine all of the ingredients and thoroughly mix. Place sauce in the fridge until ready to enjoy.