Robot doesn't drive straight

[bush]

Our robot has a 2 speed transmission. 2 CIMs turn the wheels on the left side (1 engages in low-speed, 1 engages in high-speed), and 2 CIMs turn the wheels on the right side (1 engages in low-speed, 1 engages in high-speed).

1) While in high-speed, when maximum voltage is supplied to the motors on both sides, the robot veers slightly to the left.
2) Still in high speed, if we set the motors back to neutral, the robot stops, and then it turns slightly to the left (the right wheels have a little extra turn at the end).
3) In low speed, when maximum voltage is supplied to the motors on both sides, the robot veers greatly to the left. With testing, we needed to apply about 60% less voltage to the right wheels just to get the bot to head on a somewhat straight path.

I am not sure, but I think my the solution to my problem lies within the calibration settings on the Victor. If this actually is the problem, what would I specifically need to do? If the solutions is something else, what is it?