I believe if it were his plugs, it'd do it all of the time once warmed, not every 5th stoplight or so. But who knows.

Bogging problems are always fun to diagnose

The turbo kit you have came with a fuel pump, right? So its not that..

Since you dont have any other ideas, just for shits and giggles I'd off the intake and clean the shit out of it, and all your sensors connected to it