Q: Car stalls out of nowhere

For the last few of months my vehicle has died on me while driving, no stuttering or anything like that. The engine will just turn off with no warning and the car will coast to a stop. Once stopped the vehicle will not turn over again, as if the battery is dead, however the battery is good as it has been checked. The only way to get the car running again is by jumping it with another vehicle. After that, the vehicle will run fine again until the next occurrence. It seems to be happening around the same time every month, so I believe it may die at a certain number of miles but I'm not certain as I have not taken down mileage at each occurrence as of yet. Air filter has been replaced and diagnostics at a local Auto Zone gave "ECM malfunction" code. I've read that these symptoms could be due to the Crankshaft Position Sensor needing replacement, instead of having to replace the ECM to save money and hassle as there are no Saab Dealers near me that I'm aware of for reprogramming. Thanks

My car has 150000 miles.
My car has an automatic transmission.