[Al Skierkiewicz]

Diner,
The are a variety of reasons that can cause high current in a mecanum drive.
1. The gear ratio you have chosen is too low and so the motors are not developing enough torque to drive. That puts the motor in near stall conditions.
2. Something is binding in the drive system. You may have left out a required spacer or something else is causing the wheels to bind.
3. Your design produces a lot of side load on the CIM motor shafts. These motors cannot handle side loads so any loading will cause high friction on the output shaft and eventual wearing of the motor bearings.
4. One or two of the motors are running in the wrong direction. This is especially evident if everything (current and speed) seems normal if you lift the robot off the floor. While it is off the floor note the direction each wheel is turning. If coupled in a two motor transmission, try disconnecting one motor on each side and see if the current is still high.
Without seeing your design it is hard to determine exactly what might be the problem.