I have a 99 concorde lxi 3.2 and it recently gave me trouble. It was starting and driving fine after I bought it for about 3 days. Then it started acting up on the highway like jerking and the lights flashing on and off. I pulled to the shoulder and it just stopped running, it started back up fine. A 1/4 mile down the road it started acting up again and shut off. I got a new battery in it now and i got the alternator checked twice by 2 differnt testers and it checked out good. The battery is now dead because I tried to drive it and it acted up like it was getting no power and i had to jump it and got it home. Is there anything else that I can do to avoid taking it to a shop?

is the check engine light on ?

no check engine light on just a battery light.

If the battery light is on when the car is running, then the alternator is bad. Sometimes the alternator will test good when tested on a test bench but will not work on the car. I see that a lot. I the alternator was tested on the car then the battery voltage must be 13.5 to 14.5. Any higher or lower= bad
I own an auto electric shop and have been doing this for over 20 years