While I appreciate the kind input of my helpfulness, it has been a while. Definitely do what n1dp said, check the altitude inputs. Antenna lines have cause very weird problems. They can be checked using a RFLTS. If the problem seems at exactly 10k feet, it really would be an altitude malfuntion. I need to look at some old books to see if there is a missing signal on one of the inputs that would cause this.