Combine the balsamics, soy sauce, olive oil, garlic and pepper together in a large zip-top bag. Add the beef and shake to coat.
Marinate the beef in the fridge for at least 12 hours, flipping the bag occasionally.
Before cooking, allow beef to sit at room temperature for at least 40 minutes. Remove beef from marinade, discard marinade.
To cook: We like ours on the grill, but you can smoke, grill or roast until your desired degree of doneness.
To grill: Preheat grill to 350°F. Place roast on grill, fat-side down, to sear well for about 6 o 8 minutes. Flip and sear for another 6 to 8 minutes. Reduce heat to medium high or move roast to where it will continue to cook over indirect heat. Flip roast again and continue to cook for another 15-25 minutes, flipping every 8 minutes, until an instant-read thermometer reads 130°F (this will produce a medium-rare roast; the temp will rise a little of while it rests). Remove roast from the heat and allow to rest, tented with foil, for at least 10 minutes.
When cutting, slice against the grain.