Hard Start

newb here looking for some tech help.
I Have 97 mustang GT that I just rebuilt the motor and added PI heads off a 00 GT along with full length headers new spec clutch and a Steeda short throw shifter. I started it up for the first time in two years in Jan 08. At first it would fire up with no problem but it slowley has gotten harder and harder to start to the point now it just cranks but never fires up. I have checked my spark plugs, coils, and it has a new fuel pump. I just pulled off my starter and it tested Bad. I'm not sure if this is actually my problem or if I just burned it up with me cranking the motor so much. Can a starter slowly die and cause the motor to get it harder and harder to start, or is there somthing else wrong and my starter and it burned up as a byproduct. I would love the help and cant wait to meet some more Mustang fans.

at first it would crank 2 or 3 times then fire up. now it just cranks and cranks and every once in awhile it would fire up for just a couple of seconds and then die. The first couple cranks start of slow then speeds up to where it should be fast enough to fire.