Couf horns usually have quite reliable intonation. What kind of mouthpiece are you using on this horn? In your normal playing position, can you overblow a low c, then finger a middle c, are they in tune? How about low b, b-flat? It sounds like your horn's relationship to the overtones may be off due to incorrect placement of the mouthpiece on the neck. (I assume you have no leaks in the horn) Sometimes a mouthpiece with a too wild baffle will cause loss of control of middle d as well. Let me know, I'm interested in resolving this problem. ii-V-I kenny j