Driver and stepper getting hot really fast, but working

Things were going well on my startup of printer with ramps 4.1 on arduino mega. My x axis stopped working suddenly.
I had a spare driver and that got things working again.
When I started back up, I noticed the driver heat sink and motor got hot within 20 seconds.
My other steppers do not do that.
I checked the cable and the wires are in order. Two on left are connected, also two on right.
I don't think I flipped a pair compared to other cables, but would it cause this heating behavior if I did?

I have the driver set at about 25%, same as others.
The motor turns easily when off, no friction issues.
It also travels just fine when moving manually with repetier host.
It does not make any odd noises, and does not skip or vibrate.
This must be related to more current flowing than other motors.
How do I troubleshoot this?
thanks