Art,
Sounds like the wings are twisted. The interplane struts, if placed backwards front-to-back, can cause the wings to "wash-in." So normally you want a little wing "wash-out" to avoid tip stall. Wash-in can cause tip stall. Sounds like your problem. Eyeball the TE of both the upper and lower wing. Spend some money on a good incidence checker, and examine the angle of both wings inboard and outboard and compare it to the incidence of the horizontal. Check the length of the interplane struts to make sure they are correct. I think I posted the correct lengths earlier in this thread.

I have heard other reports from folks that this plane doesn't fly right. Mine flys great with no tip stall. CG is right on the 4" mark. However, when I first put the plane together, the wing had "wash in" because I followed the manual on the placement of the interplane struts. The manual is wrong/confusing, and the service bulletin on the Hangar 9 site is BACKWARDS too!!

This plane looks awesome in the air, and is a gentle flyer with the CG in the right place. It is very touchy to land though, but it is worth it. Double check your wings again, and you might find some twist.
Good luck!