Servo and speed control upgrade might not anything to do with it. But but, it could also be the whole issue. Are they mounted in the same exact location, or did you have to place them somewhere else because of size? If you have changed the side to side weight balance on your vehicle that can change the handling characteristics of the car.
Are they the same weight as the ones you have replaced?
Did you get a bomb a$$ steering servo that has way more throw and torque? Does the new speed control have multiple settings? maybe you need to adjust the settings so that you have less torque at the wheels.
The screw in the diff will affect both side evenly or it should!
Good luck with that!!