Let me give you some more info:

VQ texan with cowl off- so cooling is definately not the issue. I purposely left cowl off for break in and my anticipated first flight, although I haven't been able to make that first flight yet due to the problems listed above.

The prop is a 10x6 three blade. Yes, the exhaust fitting on muffler is free of debris.

I have tried two plugs: one brand new Tower plug and the other a brand new Thunderpro with idler bar.

Fuel is omega 10%.

I have pretty much ruled out all the common things that could be wrong, that is why I post here. I am pretty experienced with nitro and gas engines, but this one has me stumped. I still think something is wrong with fuel lines or tank so I plan on replacing those and seeing what happens.