Without sounding harsh 967 , you need to discuss this with your LTCs as the basic principles of operating in VNAV should have been covered during your line training. Deviation from SOPs and the way the a/c was designed to be flown are the single biggest cause of jet upset, nip this in the bud, ALT hold is not the normal operating mode for many reasons.. most of which are outlined in the FMS/ FMGS sections for Boeing/Airbus. VNAV is part of an intergrated system providing much more than altitude capture.