We have a 2006 PA32R-301T with avidyne avionics. STec 55X autopilot. The autopilot will frequently begin to search for the altitude in altitude hold mode. It seems to be over controlling the electric pitch trim, as it goes from 500 fpm up to 500 fpm down. Altitude stays within 50 feet of selected altitude. We've overhauled the pitch servo, and it worked well at low altitude for awhile, but went back to searching at cruise altitudes. Anyone else have this problem, and how did you fix it? Thanks.