If it's stuttering on the camera, that's strange and could be some kind of firmware issue maybe?
If it's stuttering during playback - are you editing or viewing AVCHD natively? - then it could just be that your machine can't handle the codec smoothly. AVCHD is a good capture format, but it's a CPU hog during editing.
I edit AVCHD natively on an older iMac at work and it has some issues, but on my pimped-out PC at home (quad-core processor, 4GB ram, GeForce 560 Ti) it runs nice and smooth. You can also just convert the footage with Handbrake or something similar.