2001 Sebring LXi 2.7L
 

Looking for some help.
Girlfriend has a 2001 sebring 4 door, with the 2.7L in it. Yesterday it wouldn't start with the key in it, but the key fob would crank it. We left and stopped at another store, this time neither would crank it back. We had it towed to the house, I pulled the starter and had them check it at autozone. It was bad, Replaced it with a new one today and had issues cranking it. It would jump off just fine hooked to me battery in the truck. I pulled the battery and replaced with a new one. Now it will start on the second try. I drove it up the driveway and while driving everything inside flickers and the car half dies but keeps running. Parked it and googled issues, came upon this site.
I've been told it may be the alternator, but I know when she bought the car they told her they had to replace the computer in it, and I wasn't sure if that could be causing an issue now.
Any thoughts?