i mean you could have something there ...with the servos ....the best way to center the steering is to
1. set all steering trims to zero or the centerline on the knob
2.attach servo horn to the servo ....note you may have to adjust the linkage that the servo horn is connected to ...you want it to engage the servo right at the point that the wheels are straight ....
3. its hard to get it just right without using some trim adjustment right or left
4.still the speed at which it moves right or left should be the same ...check again for binding cuz that was a great idea that i hadnt thought of ....

finally you may have a blown cheap stock servo ...

listen to see if in the direction it moves slow if it makes any clicking popping noises....