Darn. They both have the exact same changes despite different power supplies... so it is definitely NOT the power then. I did not notice the lengths (if mentioned) in the initial post but at those lengths it really should not be an issue of power even if you WERE running them hard. Unless (as was mentioned) there is a wiring issue.
If you do not mind my asking, which driver are you using to control them?
Not sure if any of it sounds familiar, but @mario.ricci had a previous problem with these that got resolved (when involving motion).
