All of this sounds a little on the shady side ..... Who is this "Shop" that originally "tuned" it ?
If I were you I would get the SHO returned to stock asap and then look into LMS or Unleashed for your tuning needs .
If there is a meth kit on it that is not operational , leave it that way until the car has a legitimate proven tune on it ....
Meth if properly installed , makes a hugh difference on the 3.5 EB