I recently put in a rebuilt quadrajet into my cutlass 350 olds.Car was driving like a dream, But today after being in drive it was trying to die.I would put it in neutral to keep it from dying and put it in drive and it would be ok for 2 min and then start to die? I know a vacuum leak would do that to a car. but everything is connected and the hoses seem ok. What else would cause this? distributor,fuel pump? everything in the car is stock

 

try tighening down the (4) 1/2" bowl bolts. If this is a new carb / gasket the seal may have loosened up as it seated itself. Try that first. Did you replace your vacuum lines? If using the old ones, they may have developed cracking or may be leaking at the carb connections.

 

After rebuilding mine I had to retighten almost all the bolts/screws a little bit, I had almost the exact symptoms you describe. Particularly the carb to manifold bolts.