Between our weekly trips to the Baby Back Shak, the Texas BBQ Posse has been heading just east of Deep Ellum to Mac’s Bar-B-Que, 3933 Main St. in Dallas. For some strange reason, really good barbeque isn’t always easy to find in Big D, but Mac’s delivers consistently well-cooked meats and good sides from their lunch menu. Speaking of sides, the french fries cooked in soybean oil have to be among the best in DFW. Several of us have become addicted to Mac’s Frito Pie, a dish not offered at most BBQ joints. They start with a layer of ranch-style…