ORIGINAL: bafflerback
Here's a question. Does the model use a semi-symetrical airfoil? I had a student years ago build a model with the same complaint. It had a semi-symetrical wing and he built one of the wing panels upside down. You couldn't see it looking at the airplane but when we cut the wingtip off you could see that on the one wing panel the airfoil was upside down. If this is the case you will need to build a new wing.
You lost me on "semi-symetrical airfoil." Maybe this answers your question. The instructions were very specific to build the two wing halves according to the plan, WITH ONE WING HALF UPSIDE DOWN. That way I wouldn't end up with two right wings (make sense?). I was careful to do this. Is that what you're getting at?
The warp that I speak of may very well be contributing. If I look directly at the airplace from the front, and position it so that the leading adges and the trailing edge are level to my eye, one wing has the trailing edge protruding below the leading edge about 2mm for a length of about 10mm. Very small, and I have to be looking very closely to even see it. Do you think that's contributing to the problem? To me it seems very insignificant. I have faom planes that fly great with alot more warp in the wing than that, but maybe this "warp" is not helping.