Sounds like you're doing everything right. The only other thing left is to open up the 4VF and physically move the stick potentiometers until they show the same centering as your other Tx. It makes me wonder if someone has been inside the Skysport fiddling with the sticks etc. While you're at it you may want to check that they are tightened up correctly. Pots slipping round in flight can really ruin your day.

Steve