Shouldn't be tied to the CDMA or GSM as it is independent of all that. My guess is it might be a defective unit. You never really know what you are getting with a used device. Verizon locked down the GPS, but recently opened it up for BBMaps. AFAIK, Sprint did not.

Have you tried it with Google Maps or BBMaps to see if it starts and gets a fix? Keep in mind that GoogleMaps uses cell tower triangulation to figure out where you are which helps the GPS lock on as it knows where to look for the satellites.