Have your tried to use any third-party diagnostic tools such as GPS Test or GPS Status?
Whatever the GPS issue is, if there is one, it probably would not be solved by swapping units. [Edit: But if you are within your trial period, and have tested two phones with only one probelm, maybe you are the exception. So there is not harm in trying a swap.] But if there is a problem it is probably a general Samsung problem. That was the case when other Galaxy S phones had GPS problems.
What makes you think "the Samsung update" is coming? Samsung has announced that a GPS update is coming in September for the T-Mobile Vibrant and the AT&T Captivate, which were released almost two months ago. To my knowledge neither Samsung nor Verizon has said to expect a GPS update for the Fascinate. I think the presumption is that Samsung's GPS fix was already incorporated in the Fascinate release.