[exgmguy]

Try this first. Remove a small vacuum cap from the vacuum log on the fire wall and try to let the car idle in drive.
On old "E" cam trick is to give the engine a very small vacuum leak to fix the surging idle. This was a common fix before custom tunes were commonly available. Some people have good luck with an idle air bypass plate as well.

Did you reset the ecm after installing parts? It is also a good idea to let the computer relearn the new characteristics of the engine.