Starter? 07 6.0

[jet6122]

I've had ongoing problems starting my truck. The seller put in an alternator in July. Since I bought it in September I have had long cold starts and a no start. I've gotten good advice here that led me to getting the reflash, then a pair of batteries and another alternator. The truck was doing great until a few days ago. I went to drive it the other night. Cycled the G plugs. When I turned the key, nothing happened. The radio came on and the headlights were bright. I kept turning the key on and off, finally the the motor turned a little, then started spinning and cranked. The rest of the night it cranked fine. It did this before the newest alternator as well. I went out to drive it to the shop yesterday and can't get it to start spinning at all. The voltage on the batteries are good (12.94), and whacking the starter with a hammer didn't help. I think also read in this site that a bad alternator can damage your ficm??? Any ideas? Thanks again.