I'm at my wits end with this car.

I drive home yesterday, everything is fine. Get in my car an hour later, and it wont start. I hook it up to a friends car for a jump, and after 25 minutes I can finally get it to start. I drive it about 20 minutes and as soon as I turn my car off, my lights start flickering, so I try to turn it back on, and it's completely dead again. Get another jump, and after 20 minutes, I get it to start again. I get it back home, does the same thing, lights flicker.. dead.

This morning I tried to jump it off my friends truck. I had it hooked up for a good 30 or more minutes, and couldn't get it. I took the battery out, and took it to get tested. They told me it was dead (surprise) but it was not a bad battery.

When I try to start it over, it turns over one good effort, then one half assed effort, then nothing. The lights, inside and out, flicker, the gauges flicker, and the radio that I finally tuned to my liking a week ago, keeps on getting reset.

A couple weeks ago, maybe even a couple months ago, I pulled a code that said something about a LF door circuit high. It didn't seem to be causing an issue at the time, and when I went to the shop last week, I asked them to look into it, and they told me they would charge 80 some bucks to do it, so I said no thanks.

I did take it to the shop exactly a week before the problems started, and had the ignition cylinder replaced. I was having a security problem, I'd start the car and the security light would come on. Sometimes my car wouldn't start, and I'd have to wait 10 minutes for it to start.

Its a 2003 SS by the way. Sorry it's so long, trying to give sufficient info.

Any advice would be great.