Closely trim fat from brisket and place in basket, lightly season both sides with black pepper, garlic & onion powder, cayenne, and heavily with paprika. Place in Rotisserie and turn both burners on as low as possible. Place a few mesquite chips right on the grill. Prop grill hood so the front is open a good 10 cm and let cook while preparing sauce.
Texas BARBECUE SAUCE: By: Susana Montes, modified by Steve Shanker Melt the margarine in a saucepan, add the onion and garlic, and cook over low heat for about 5 minutes. Add the remaining ingredients, except beer, and simmer for 15 minutes. Add beer, and simmer for another 15-20 minutes. Remove from heat, and use for barbecuing pork or beef.
After grilling for about 30 minutes, generously coat meat with sauce. (I continued to cook sauce maybe another 10 minutes longer after this) Continuing grilling (4.5 to 5 hours total time), basting every 30 minutes or so. Add a few more mesquite chips every hour or so. Sauce will form a glaze on the meat keeping it from burning.
Remove meat from basket and slice meat THINLY on a bias (meat should actually fall apart as it is cut)...serve with remaining sauce.