Special K '98 T/A

I have a 1992 Z28 350ci TPI and when I go to start the car it has to crank for about 10 seconds sometimes before it will finally turn over... ?? anyone have any idea about this?? someone was telling me maybe it's a bad relay?? but which one?? and where do I find it to replace it?? this problem is really aggrivating when I'm trying to start the car b/c sometimes it will take a couple of tries before it will start up... I just replaced the starter in it (the old one died on me) and I have a feeling this long cranking time is killing my starter again so any help would be greatly appreciated thanks