I had the same problem with my Max-ZOne scope last year. Everytime I think I had it sighted in it would start shooting a few inches low again. I kept re-sighting etc.. finally my scope adjustment knob was turned has far as it would go.. couldnt adjust it anymore. Throughout the whole process it cost me 2 deer (not wounded, flat out missed) and a headache. Switched back to pin sight for the rest of the season. Now have the Vari-Zone scope and have had zero problems. I believe there is a rare problem with the pins in glass moving somehow... dunno. I would switch back to the fibre sight and see what happens, i have a feeling your headed down the same road i did.