Punisher GTO

I just had a new 96MM intake installed that I had ported with a 92mm fast TB, I also had this tuned as well.
The car idles fine at a complete stop right around 1K RPM

However once you put the car in Drive you can take your foot off the gas and the car will move on up to about 40MPH (on a flat road)

Now once the car is moving to about 30-40 MPH the car stutters and the RPMS drop a little just for a second then it kicks back up.

Now I was doing 40MPH and I needed to slow down (speed limit was 30MPH) so I got tired of hitting the brake so I put it in Neutral to let the car slow down. But while I'm in Neutral the RPMS jump up to about 2.5K.

however if you have the car at a complete stop and put the car in Neutral the idle is fine.

I was looking over the intake to see if there was a vacum hose that was loose but I couldn't find one. I did hear a very faint hissing sound coming from the intake but I couldn't tell if the noise was abnormal.

I'm thinking that the stuttering I'm getting is from the stock stall on the car because when it's stuttering the RPMS are around 1.2K so I figured it's the stall.

but I can't figure out why the RPMS are so high in Neutral when rolling.

Any thoughts?

ss.slp.ls1

iTrader: (36)

My first thought was air/vacuum leak. I have heard that you can take a can of carburetor fluid or any combustible aerosol and spray it around all the seams of the intake and TB and wait for the rpms to climb. Then you've found your leak. I have also heard of performing a smoke test.

hellbents10

iTrader: (10)

Ported throttle body, Log your IAC counts and see if they are at zero.

PREDATOR-Z

sounds like vacuum leak