My Caprice is driving like crap, HELP!!!

I just bought a 1993 Caprice 305 5.0L V8 and whenever i am in reverse or when I am coming to a stop it starts to sound like it is gonna die and my lights dim in and out. Sometimes it does die. Whenever I am driving above like 10mph it drives fine though.

I've looked through the site and have read alot of different answers( Opti-spark, Cat, New carb gasket...) and I was wondering if anyone with my year and engine have had the same problems and how did you fix it.

My mechanic friend gave it a tune up and he told me that my cat. needs to be replaced and since the guy I got it from let it sit for a while that I need to drive it and let it clean itself out. But it doesn't feel like that could be it. At first I thought it was the timing but we adjusted it and it still drives the same.

PLEASE, I call upon the Caprice experts, Gods if you may, please HELP!!!

The cat makes sense... ta clean it out, take the car out to an open road and floor it. I mean bring the car to about 100-110 mph. Seriously, you'll be amazed at how much something that seems so wreckless can help a car. It should give the car a smoother idle, and faster accelleration too. If that doesn't work, then your cat might be too badly clogged, and would need to be replaced. Also try running some carb or fuel injector cleaner through your system.

Vacuum leak will do the same

Yeah, I used some Valvoline fuel injector cleaner. I took it to a back road and went about 90mph for a solid 6 sec. But, yeah does anyone know where I can get a good cat. converter for a good price. I'd like to get like a high flow one if they make 'em.

I do not know about high flow cats, but I have found places to order Chevy Caprice parts (including cats):

http://www.chevypartspro.com/
Select your year and model and it has some stuff including cats.

https://www.rockauto.com
This is the best site for Caprice stuff I have found so far. It has almost everything you could need, way more than most sites.

http://www.uneedapart.com/index.php
This site has used parts.

You could also try www.Summitracing.com, www.Jegs.com, www.jcwhitney.com, www.paceparts.com and www.edelbrock.com/automotive/index.html, but I do not know if they have parts that will work for the Caprice.

Let me know if this helps