Searched and only found one post with similar issue but car mentioned had more miles than mine. Here is the issue
2004 Touring Automatic
Mods: Z1 5/16 plenum spacer, Stillen high flow cats, Topspeed Pro 1 exhaust, Roar intake
All were on the car, with the exception of the plenum spacer when I purchased it one year ago with 27K miles on it. From the beginning the car has stumbled for ~0.5-1.0 second on hard launch and then will smooth out and pull strong. Car does not do this when placed in "manual mode". Any suggestions as to where to look.

Related from search done: Is there a safe method for cleaning the MAF anywhere?