Zoned,
If i understand correctly, you are saying if the plane is on the ground it will run fine but once airborn it will stall..
maybe there is excessive vibrations to the tank while in flight which are causing air or foam to go through your fuel line resulting in a hot run untill dead stick. Something is happening in the air that is not happeing on the ground. It could be a number of things.
The prop is so off balance that in the air it shakes the whole plane.
the vibrations from the eingine are shaking the tank and causing foam.
whne the plane comes down dead, is the engine too hot to touch?
is your tank surrounded with foam?
have you chekced the clunk line in the tank? that's something I always find problems with on my planes..
Have you checked to make sure the clunk is still attached to the line?