Giant 20' x 3' x 2' router build

[JAZZCNC]

That's not hot for steppers so don't worry too much about it. Esp if they are moving slow rather than stood still as they will be using full torque to hold position
and not going into current saving mode.

Are you sure the drives are set correctly regards Amps and motor setting.?
What number or letter is the dial set to on the drives.?
Have you tuned the drives using protune or just using the dip switches.? If not try to use protune and make sure the amps are set correct for the motors. Wrong amps setting would cause this problem and the drives default to a low setting if I remember correctly. If you have the wheel set wrong on the drive it will think it's using differant motors and can default to low amps setting and wrong PID tuning in the drive.
Do the motors make any whistling or loud buzzing sounds.?

150 on acc is far too slow for any z axis and you should be able to go much higher without any trouble. So this must be either your set wrong in the drives or there's binding at some point.!