Probably need to get it re-tuned. If all they did was load in the stock tuners tune, then that would be part of the problem of the bog. The Standard tuners tune bumps up the top end a bit more but takes away a bit of your torque at the start of your rpms. But even Stock SVTs had some bog at the beginning.
Tunes fix that, if they are probably tuned. Did the last owner give you the tuner with the purchase?
If so, find Tom on here and PM him. Ask him to help you with the tune for your car.
Not to pricey, and will help you with some of your performance issues.