Its got to be the tune. sounds like to me the load values are off. here is another guy haveing similar problems. if i had a log or the ecu i can take a look at it.
http://www.svtperformance.com/forum...5160-breaking-up-under-hard-acceleration.html
considering more then 1 shop has tuned it and that link has no relation to the issues he is having, i would disagree.... as a matter of fact, you do realize that this issue existed BEFORE it ever came to our shop? This happens when you go to accelerate from ZERO MPH to 5mph... this has NOTHING to do with breaking up under boost etc...