Oceanic VT-3 elevation probs

I have a vt-3, this will be the start of the 3rd summer of diving with it. Untill now, all of my 100+ dives have been at altitude in fresh water (Montana). I recently moved to Kailua Kona, Hawaii, and now I am having problems. My vt-3 flashes "el-2" instead of "sea" indicating that the pdc thinks I am at altitude. On top of that, when I get about 20 feet down, the pdc then ends the dive, and starts my surface interval. It will eventually switch back to saying I am under water, but give me a depth of 7 or 8 feet when I know I am still around 30 feet down. Then when I do surface, it will say I am still diving, at about 7 feet and not start my surface interval. I have installed new batteries, but still the same. Any advice?

I just took the new battery out, let it sit without a battery in it at all for about an hour, then put an all new battery in again while I was at sea level. Now it says el 5, I dove with it down to 30 feet, sat in one place for about 5 mins and watched the depth guage. It would go back and forth from 15 to 20 feet (giving me an allarm that I was ascending too fast) while I was staying completely still.

I would soak it in warm water and 25 % vinger for 15 min. If that does not fix it it time for the service.