Did your car have a tune prior to the turbo replacement?
The dealer could have updated the factory software to the latest version, which a lot of folks do not like.
the combination of no aftermarket tune and the new factory software version could make the car feel slow.
2011 Mineral White M3 ZCP
Paint Correct, Opticoat, Ventureshield, some CF, B&B exhaust, AFE Intake