My daughters car dies typically after about 30 minutes of driving. Sometimes way longer. Sometimes not. But mostly. Just shuts off. No warning. No low idle. No stalling. New alternator after the last one tested mildly bad. New connectors for the terminals. New belts. She had some corrosion. Totally clean now. Not a fuel issue. A silinoid issue maybe? Is this common? We've tried everything. Mechanics are only charging us at this point with no answer.