im going to say its turbo lag. I have noticed the same things u guys have, remember its a big turbo on these suckers. with the stock tune its not so bad but the more boost you use the more lag you will see as there is more power with more boost so 4 psi feels slow untill 15 psi kicks in. a custom tune will allow more boost to be added lower in the rev range and give you the kick your after most generic tunes have a fairly soft boost curve. removing the stock blockagecooler/intercooler will help too. some will say im wrong but a bigger cooler and pipes makes boost earlier with better throttle response.