That's usually the best teacher.
Did they replace the HD? As CM mentioned, going from a fast drive to a slow one will slow things down. If would also be interesting to know if you got a "like" component for component replacement. It is not outside the realm of possibility that lessor parts were substituted. Not trying to lay blame (or even suggest that's a standard practice - it's warranty why should they) on BB or GS, but such things have been going on for millennium.
Good luck.
Supposedly they only replaced the motherboard.