[baumgartensam]

What I would recommend doing is printing out your X and Y input and then your wheel outputs. Confirm X and Y are in-fact what you intend and then check that the correct wheels are moving. If that doesn't work, you could always subclass RobotDrive and then override the following methods:
public void mecanumDrive_Cartesian(double x, double y, double rotation, double gyroAngle);
public void mecanumDrive_Polar(double magnitude, double direction, double rotation);

If none of this works, could you make a codebase with only drive code and posting it here?

Good luck!