CDA,
I think you are on the right track. The problem is most likely in the gun it's self. First remove the grips and try the mags, if they now drop free, you've found your problem. Check for drag marks on the magazines,(long grip bushings or screws) if there are none, remove the mag catch, and see how freely your mags slide in and out of the pistol. If they move freely with the mag catch removed, replace it.
Savage