As others posted above it does sound like too much elevator throw and possibly and AFT CofG.
Although if it IS balanced too nose heavy, the amount of elevator required to try and hold the nose up at low speed could cause an accelerated stall.
In recent model magazine articles the proper flight test methods have been illustrated to help you to determine how to make your plane fly better. They show how to check for proper CofG and engine thrust and decalage. Using those methods may be of some help for your Spitty.

I would also suggest that before you go and use the computer radio to adjust the response of any surface.
That you FIRST adjust the mechanical linkages to get as you can to the desired results. THEN use the convenience of Expo and Dual Rates.