yes... the name plate voltage of a stepper motor is generally much less than what the motor is supplied with, expect it is switched at a high rate to avoid motor heating (aka melting it) check out this link for some great background on how to power a stepper motor (click stepper faq)
http://www.geckodrive.com/ark-4/faq.htmledit -- i re-read your post, i'm not sure this applies to 5-wire steppers... :/ sorry
edit 2 -- my personal experience with low torque motor problem was a blown driver chip.
good luck