I have a 3-9 Trijicon acupoint mounted on a 7 Rem Mag Tikka that will not hold zero. The last time I had it out hunting was the late Deer season in early Jan 2010. I missed two deer and switched guns. After the season was over I took it to a local range. It was 4" low and 2" right. I sighted it back in and put it away for the year. TI took it to the range today to check it out. The first shot was 2" low and 2.5" right. All shots were taken using a rest and a concrete bench at 100 yards.
Sighted it back in at 1.5 inches high at 100 yards. I then bounced the rifle 3 times. I let it drop about a foot on the concrete bench. Next shot was 4.5" low and 1.5" right.
I checked the mounts and they were all tight. I am using weaver style bases and millet rings.
Any ideas?

Yes, I had a similar problem with my one and only Trijicon. Gears stripped. I sent it back Trijicon and they fixed it.....and then I sold it and bought a Leupold. Problem fixed.