I just got my 91 Blazer back from garage number 3 and it just made it home before it burnt up ANOTHER coil! I have been thru 7 coils in a month. They have replaced Distributor, HEI Module, Cap, Rotor, Plugs and Wires, MAP Sensor and cleaned grounds. The only thing not replaced yet is ECM and ESC. I am at wits end. I was hoping someone here could give me some help. I guess I will try the ESC and ECM myself, and if that doesn't do it, I don't know what to do. Ideas?

High resistance is what burns them out. Resistance from the surface where the ignition module mounts, (inside the distributor), to the battery negative terminal must be less than 5 ohms. If greater than 5 ohms, check both negative battery cable ends and both body ground cable ends. If necessary, you can run a 14ga wire from the distributor housing to the negative battery terminal. Couple of inexpensive checks you can try.