Chevy 350 dies after startup--won't start for minutes

Hi all...
I installed a brand new 350ci/290hp crate motor about a year ago. It didn't run great with the old Quadrajet, so I put on a new Edelbrock 600cfm/electric choke/vacuum advance carb. I used an adapter plate to mount
it. The EGR valve is gone, and blocked off with a plate. The emissions control stuff (minus the Cat) has been taken out of the equation ;-)
Basically, I start the truck, and it idles as it normally does when started cold after sitting a while.
Regardless of whether I take off immediately, or let it warm up a bit, it'll die after about 30 seconds, more and more frequently. When it dies, it's a real struggle to get it running again. When I do start it, there a 50/50 chance that all the fancy footwork in the world on the accelerator won't keep it running. Even if I do manage that, there's no way I can put it in gear....it'll die immediately. Sometimes after 2 or 3 minutes, it'll start and run as normal, today when I was attempting to leave work, I was stranded for 15 minutes.
Here's some additional info: When I was at the doctor's office about 3 weeks ago, I started it, backed out of the parking space, and then the truck died. I managed to start it, but had to be tricky with the gas pedal to keep it running. Again, putting it in gear was out of the question. I finally found a comfortable spot to keep my foot rested on the pedal, and I sat there giving it gas to keep it idling for about 15 minutes. After that, the idle speed suddenly surged up, and I took my foot off the gas. It ran fine at that point.
It seems to be getting fuel just fine. The filter is a clear glass one, mounted right up in front of the carb. It's full of gas, and when I try (sometimes in vain) to start the truck after it dies, I can smell the gas coming from the tailpipe. It seems to be getting plenty of spark and air. The choke seems to be ok (as far as I can tell).
The only explanation I can come up with is that something, somewhere is getting stuck...hence the 15 minutes of running like crap followed by everything suddenly being just peachy.
I will add that "running just fine" for this truck isn't exactly great. It's run EXTREMELY rich since I got the new motor and carb. The timing is advanced to (don't laugh) like 14 degrees BTDC at idle (really!). I have never managed to lean out the mix. I think the rich running condition and the weird startup problem may be related. The startup problem occured like twice in the 2 months leading up to this past month. Lately it's occured every 3-4 days, and getting more frequent...
I know this was a long post, but I figured I'd provide the best description of the problem I could.
I'd appreciate any suggestions as to what may be the cause of this.
-- Regards,
Jon R. Pickens / jonrpick at yahoo dot com Catch me on Yahoo or AOL Instant Messenger, screen name "jonrpick" on both.
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Sounds like it is getting choked out to me. Too much gas. Do you notice a rich smell from the exhaust?

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Well yeah, it's been extremely rich since I got the new engine and carb... This occurs at idle or while driving normally.
Either way, why would the problem suddenly clear up on it's own???
Forest Hursey wrote:

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----Carb Ice----are you running any form of carb heater? What about tuning the carb for correct mixture? Start there then post back
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carb icing probable if you are not running any sort of intake heater (stock air cleaner snorkel had thermostatically controlled flapper). carb ice can occur 60-68*f with just the right humidity any one flying light piston aircraft could fill you in as this is taught in ground school
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