Does the engine quit while it is developing high power, or does it quit at idle, or low power operation? If it quits while developing reasonably high power, and the glow plug is still good, it has to be a fuel problem. Go over the fuel system again and check everything. If you don’t find anything obvious, consider the circumstances. Does it quit when maneuvering or sometimes when straight and level? If it’s only during maneuvering flight, what maneuvers? Positive or negative g’s? How is the fuel tank mounted?

If it quits during low power operation, adjust the idle mixture and/or increase the idle speed a bit.

It doesn’t sound like an engine problem, more of an installation thing.