Michael, the simplest solution to the erratic trim behavior on the keypad is to program two of your joystick buttons for elevator trim....one up and one down.   For some reason, the sensitivity and delays using the keypad are not as pronounced using this method.

You also have to understand that trim corrections require a few seconds to take effect because of the small size of those tab surfaces.....and are very sensitive to changes in airspeed.

As a last resort, you can change the sensitivity/effectiveness of the elevator trim with entries in either the CFG file, AIR file or both.  Doing this is a bit more complex and depends on the individual aircraft's file setup.