The most common reason shrimp are dry or tough even when sitting in a succulent butter sauce, is that they are simply overcooked. Shrimp cooks very quickly. They need as little as 2minutes on each side.  The best way to avoid overcooking is to have everything you need ready and close at hand while cooking. Also, plan your cooking order so that the shrimp is the last thing that needs to be made so that it can be served immediately.