Hmm, I did not see you mention fuel filter - I certainly hope you have one! I speak from expreience when I say that a leaking filter is bad news!

Other possible sources of leaks: does the venturi have a gasket? Is the gasket seated? Is there a leak path between the venturi and the crankcase? that can ruin your whole day too! My brother was fighting a losing battle with an old Veco 35 until he discover that leak. He then glued the venturi into the case using silicone and the problem went qway. Ditto the NV assembly - make sure it is not leaking around its base.

Took me a long time to reach this point but I have become a believer in muffler pressure - I think it could have a positive impact for your situation.

Don't be afraid of changing glow plugs either. My favorite continues to be the K&B with Fox a close second.

Having said all that I have, I cannot claim to be any kind of expert on high-altitude engine problems. To me every engine problem usually boils down to the engine getting fuel, air, and fire. If the engine is sound it MUST run....

dennis a