In case you haven't figured it out yet - switch the channels the servos are plugged into. If the problem stays with the servos, one is bad for some reason. If the problem stays with the original channels, the problem is likely in the radio programming. (Assuming the linkages are the same.) My other guesses could be one linkage has a LOT more drag in it, EXPO is not the same in both channels, and make sure there is not a premix that you are not aware of affecting the two channels.