You stated the engine died when inverted with 3/4 of a tank. This leads me to believe you MAY have an air leak somewhere.

I suggest doing/trying the following:

1. Replace ALL the fuel lines on the engine and in the fuel sustem, including the line from the clunk.

2. Check the o-rings on the needle valve - replace if they look worn or are hard or cracked.

3. Make sure the back plate and carb are seated and not leaking air. Sometimes the engine will run good on the ground, but the vibration in the air (it is a slightly different type of vibration ) will allow air to leak past the back plate and/or carb. A little bit of silicone cures that problem.

4. I know you said the glow plug was new, but check it anyway. It should glow a BRIGHT orange/red AND ALL THE COILS should be glowing. The OS #8 is an excellent plug for the 46 AX.

5. Try a different fuel - perhaps 10% nitro. Someone at the field should let you try a tank full of theirs.

6. Make sure your muffler to fuel tank connection is tight.

7. You said "The engine still starts good, picks up rpm but then takes a second or two to peak. "
This IMPLIES that your transition (idle/high speed ) adjustments may be off a little. The engine should go from idle to peak in a smooth manner, with no hesitation, coughing or stumbling.

You need to peak the engine, THEN BACK OFF ABOUT 1/8 TURN (about 300 - 400 rpm ). The engine unloads in the air and if you have it peaked on the ground you may be leaning it out in the air, especially if doing any type of manuvers.

I have found that the best way to check this out is:

After the engine is adjusted, with the engine at full throttle, pick the plane up and point it nose up and hold it there for about 10 seconds. The engine should stay at the same rpm. If it changes rpms the high speed adjustment if off.