Preparation
Trim fat from meat. Place meat in a plastic bag set in a shallow dish. For marinade, in a small bowl combine orange juice, lime juice, garlic, sugar and oregano. Pour the marinade over the meat; seal bag. Marinate in the refrigerator overnight, turning bag occasionally.
Drain meat, discarding marinade. Place meat on a rack in a shallow roasting pan. Insert an oven-going thermometer into the center of the meat. Sprinkle the meat with salt and pepper. Roast in a 350 deg oven for 45 to 60 minues or until thermometer registers 155 deg. Cover with foil; let stand for 10 minutes before slicing. (the temperature of the meat after standing should be 160 deg)