I've had pitch control problems with my 235.. Did two things, replaced the altitude transducer and opened the newer transducer to the cockpit with a small air filter attached.   All is well, response is dampened and controls within 10 ' or so..  
  In S-Tec's behalf, they have modified their test trocedures to cach low resistance readings on transducers and have refunded its repair cost. My old one read 2 to 10 ohms, the replacement was about 15K ohms..  Thx Van.
  Don Skeele  N320J