I've read the info on this topic here and have tried the simple stuff that people have said can fix this. Specifically:  (1) The system ground tests fine per the manual  (2)  the cables from the tail servo are at correct tension levels (tested at annual)  (3) pitch controls are well-lubed and not binding anywhere (4) avionics guy sprayed contact cleaner in the servo Next step would be to pull the tail servo, bench test, possibly send back to STEC to overhaul / replace.  I'm may be look