Yeah Jim,
I've seen almost the exact same thing on an 80" Sukhoi.
I started out with one coreless servo on the elevator. Not enough torque and very spongy feeling. I went to two JR 517's and it felt the same, but with tracking problems in loops.
I put in two Futaba 9304's and it was very acceptable. Now I have two of the low $ Hitec 5645 digitals and the increased torque at low deflections was very noticeable. It felt like I turned my expo off. Unfortunately they don't center as well as the coreless Futaba's. They find a different center from each direction of deflection.
Pull an up elevator manuvuer and it needs a click of down trim afterwards. Vise-Versa for down elevator.

On rudder I have went from 2 517's (not enough torque or centering accuracy) to 2 9304 Futabas (not enough torque) to 2 JR 4721's (closer) to the current one JR 8411 digital with a bellcrank dividing the 125% throw into +/- 45 degrees.
It still feels like it may need just a touch more torque in some knife manuveurs.
I am thinking about trying one of the Hitec 1/4 scale digitals, but I don't know if it will center as well as the JR 8411 does.