I had stabiility issues with my ST4000 when I installed it. I got the following advice from Raymarine. After making these changes, I have had trouble free operation for 3+ years.
If you did not get a reading of 10 degrees or less, try re-doing the linearization immediately. If your Catalina is in the neighborhoood of 2 or fewer turns of the wheel to go lock to lock, change these 4 settings in the Dealer Calibration page in unison to the following:
Rudder Gain to 2
Drive Type to 2
Response to 2
AutoTrim to 2
If your Catalina has less than 2 turns lock to lock, you may eventually drop the Rudder Gain down to 1, but bringing these four settings to 2 initially should get the boat under control so that the other adjustments are just tweaks to your boat's individual handling characteristics.