Engine Stalling

im in same boat when u start losing collant with no noticable leacks usually its a blown headgasket . not an easy fix but can be done with decent set of tools and some patience. the trick is to make sure u purge the system when u refill it with coolant other wise a steam bubble in the system will cause the problem to probably happen again id recommend doing both headgaskets when u dismantle it so as to avoid "doing the other side" later hope this helps

Is this still happening and did you find out what was causing the problem?