if you cant get it figured out in software, try checking the pot inside your servo, it tells the servo board where the horn is pointed, iv had them go bad before and its a pain to figure out..
i dunno what type of servo your using so i cant give you any values, but take the pot and remove it, hook it up to a multimeter and spin it very slowly from left to right. the curve should be smooth. iv had pots that jump all over the place. bad pot...
Good luck
Truckstop