[Justin M.]

The CIM motors have neutral timing, so they don't favor one direction with slightly less RPM's.

You always have to reverse the polarity of one side of the motors driving the thing, either in the programming or by just simply physically reversing the polarity from the Victor. That would explain why your robot wont go straight. If the left side motors are turning left, the right side motors will turn left as well, but turning left on the left side motors means that turning left on the right side motors (which are inverted), will actually appear to be turning right, due to how it's mounted on your chassis.