Everybody has come up with all good reasons for an engine quitting. There are so many things that can cause it. I myself went through the same aggrevation when I tried using up 3 year old fuel. Some was even 10 years. Old fuel has had a chance to absorb moisture from the air, not to mention the nitro become very unstable and dangerous with very old fuel. My engine would tune fine on the ground, take off and fly for a while, and then suddenly dead stick. New fuel cured that problem totally. Obviously you're probably using fresh fuel. Another thing you may want to consider is using a fuel pump. It's possible the whole setup you have, while functionally okay, may not be supplying enough fuel at high throttle. You can test this by attaching a squeeze bulb to your pressure line, run the engine, especially pointed up, and have someone hold pressure on the squeeze bulb. Tune the engine and throttle it up. If it stays running, good. Then put the pressure line back on the muffler and check again for quitting. If it does, then fuel flow would be a likely candidate. These are just a couple of ideas. Might help, might not. Good luck trouble shooting that problem.

p.s. Those Enya glow plugs are awesome and I have cured many problems just using them. They are not cheap, but worth it.