I'd have to check voltage and ground circuits for the starter. Any testing at the starter, make sure tranny is in park or neutral and the parking brake is set.
Two voltage circuits at the starter, one is battery voltage, hot all the time. The other circuit goes hot with key in the crank position and is wired through neutral switch for automatic tranny. The starter grounds through the engine block. If those circuits check out ok, could be issue with starter itself? Some of the national brand auto stores will test the starter for you, if you take it off and take it to them.
Another thought is your security system, where applicable. Some security systems can effect both starter and fuel injectors others may only effect your fuel injectors. Just a thought.
I realize this is an old post. You probably no longer own this vehicle. In the future, hope you don't have any vehicle issues, but, if you do, keep the site in mind. They are always trying to improve the site and it is free.