Massive CPU usage in cubase 5

Recently i bought a macbook pro so that i could use Cubase 5 properly. My old computer was old and did not handle DAWs so good (not at all). However, when I record using Superior Drummer 2 and Guitar rig 5 (only recording 3 tracks) my CPU is at about 95%. Ths is even more than what CPU usage my old, crappy computer had. Anyone knows what i must have done wrong? It is really annoying to have crakling, lagging etc, etc, when I record 3 tracks to a midi track.
Any advice would be much appreciated.

Need more info. Computer setup, OS, which C5 version etc.