Wow that is frustrating. You did everything we all would have done. I an not sure why you changed the ign voltage however, 5.1 v is fine for that pack.

You still might have an ignition problem, it is possible that the circuitry is sensitive to heat and after some buildup it cuts out. I have seen this once in a CH module, we chased a fuel problem for days and when we swapped modules the problem was fixed. The new 3W ignition is pretty rock solid however.

I find it hard to believe its a carb problem since the engine runs fine at full tank BUT I have seen some screw problems with those tillotson carbs from time to time. When the tank is full there is no air and at least some gravity feed. If the pump diaphragm is weak it may not be pumping correctly when the fuel level drops. Any time I had one of those carbs act up I put on a Wallbro - same one that's on the DA. Problem fixed.

I normally don't recommend this, but you might want to ground run it for that amount of time and see if it still happens. This would confirm the ignition and probably rule out the carb. Keep and eye on the heat buildup though.

Stinks to have to do this but you might want to send the engine in for a checkout. Dead sticking that plane at the wrong time could be really costly.

DP