Weird Engine shut off problem

Ok so here it goes, and this will probably be long so bare with me here. I have a 2004 mitsubishi lancer es 2.0L, this is an off and on problem and when I take have taken it in they can't quite seem to find the problem and tell me everything is fine. I have 152,304 miles on it.

I've had the timing belt/water pump replace, I get my oil changes done every 3,000 miles(this is a one owner car bought brand new), had a tune up(spark plugs and spark plug wires), had the egr valve replaced because it was throwing a code(or so they told me), oxygen sensor was replaced(although when I left the place wasn't sure if he replaced one or if I have two), had a new radiator and battery replaced. Fan control unit was replace also and I had them do the throttle body cleaning. Head gasket was replaced at about 80,000 miles.

Problem is every month or couple months when I am stopped for too long the engine just cuts off, I can turn the key and it turns on just fine no issues and will drive another month or two with no problems.(no shuttering it just cuts off, radio works and lights)

My check engine light is on and when I took it in he told me it was my catalytic converter( I will replace that soon) and I do need a front motor mount as well. I was told that the catalytic converter wouldn't cause any driving issues and to just replace it before I get my smog check done. Had the alternator checked out and it was fine too.

I'm really going crazy trying to find out what the issue is, an vacuum leak somewhere or something more serious. I don't get cheap gas either and never have and I do use fuel system cleaner every oil change.

Thank You