New edlebrock help

[BigRed Beast]

My son's truck, a '72 Blazer.

We've been through a few carbs in the past two years, so we finally broke down and bought a new Edlebrock 1406--600cfm w/ electric choke. it's on an Edlebrock manifold, stock 350, mechanical fuel pump with a 38 gallon fuel tank.

Bolted it on, started right up, a couple adjustments and he's off. Less than a week later, he's broke down in the school parking lot, no start, gas pouring out of the carb. I should also note that those are the same symptoms of the Quadrajet we just replaced.

It's his daily driver--or was--so I can only repeat what he said he observed prior to the break down. He mentioned that it was hard to start when warm; that he had to play with the accelerator when coming to a hard stop to keep it from stalling. His tach indicated about 7-800 rpm at idle.
Also, we are in the Denver area, so altitude is above 5000 feet.

First, am I looking at a carb issue, or is there another culprit? Second, if it is a carb issue, are the stock float settings suspect, and is the Quadrajet similarity just that--a coincidence?

I know you guru's have some thoughts, and perhaps need more info to help trouble shoot...fire away!