Car stumbling and dying

[DRJDVM's '69]

Hey Guys
I just put a new small block 434 in my car with a Pro-systems carb built specifically for my application. I've got just over 450 miles on the motor so far, but am having issues with the idle.

The car takes awhile for it to "warm up" until it will idle on its own, then seems to run fine for ahile where it will come to stop and idle but then after I drive it for awhile, when I come to a stop it wants to die unless I feather the throttle to keep it running...

For example....yesterday i drove it to work. When I first leave my house I need to keep tapping the throttle to keep it idling. The I get a couple of blocks, it idles fine. Get on the freeway for about 15 minutes, then off and through town... a couple of stop lights through town it wont idle when I come to a stop....it wants to stumble and die unless I feather the throttle.....

I havent pulled the plugs yet, but that was next.

I plan on getting it dyno tuned to really get it set up right, but want to put some more miles on the new motor and clutch etc before I really beat on it. For now I just want to get it to idle around town...

So any suggestions on what to try first ??