Dying Dart after being warmed up.

When it shakes and dies at idle, especially when shifting from P or N to D or R, it is usually from running too lean. A vacuum leak can cause that since it becomes much more significant at idle. In my case, over 17 years, the problem was the Holley 1920 carburetor. After the ~4th one, it idled perfectly smooth and no more stumbling off the line.