Place pizza stone on grill light burners and turn to low. Allow grill to slowly heat up to about 300º. Turn off burners directly below pizza stone, and adjust heat to maintain approximately 300º. 

Place the roast in a heavy roasting dish. Sprinkle the vinegar over the roast. Season with salt and pepper. Place on the pizza stone and slow cook for 1-1/2 to 2 hours. Remove roast from heat and allow to cool down a little.
 
Depending on how tender the roast is, either shred with a fork or it may be necessary to cut the roast into strips and then shred by hand.

Place the beef in a lightly oiled non-stick pan and add chilies, garlic and onion. Sauté until onions and garlic are soft. Use in tacos or burritos.