Run of outs

I HAVE a 2001 Commodore SS. Three months after I picked it up it was returned because of a faulty oil pump, and the motor had to come out. From then on I've had numerous problems, from the airbag light on the dash coming on twice, a side electric window not closing properly, the indicator arm shorting, the fuel gauge not registering properly when the tank was filled, the traction control light coming on while driving and failing to go off until I stopped the engine and restarted it. I've just completed an oil consumption test with the new motor and I've noticed severe clunking noises from the diff. I was told by a Holden service centre it was diff chatter, but have now been told I need a new diff. For a three-year-old car I find these problems unacceptable. I've been told I will have to wait five weeks for the new diff and that I can still drive my car. I am now finding it is hard to get into first, second and reverse gears. Have I got a lemon or what? Should I demand a new car?