My autopilot has been working fine to track the GPS course and hold bug altitude in EFIS mode until recently. With both my 3400 and 4500 set to LAT NAV and VER ALT the AP button will not show EFIS and track the selected course when pressed. Works fine on AP to hold selected altitude and selected heading but can't get it into EFIS mode, simply stays in AP when I press the button to try to get it into EFIS mode. Ideas?