I hope you have already sorted out the problem, but if you haven't I give you some tips.
The best way to upload your HD videos to youtube is to take few steps before actually uploading videos. For example, I have also an HD Video Camera and upload HD videos, but I never upload raw footage which is in AVCHD format. I am not 100% sure, but youtube doesn't support that. The best way is to convert your avchd files into other file formats such as DVD, WMV,FLV,DV,MPEG2 etc. Once you do it, the problem will be gone.
I have used different video editing softwares, but for HD Videos, Corel Video Studio 12x Ultimate is the best one. If you need any help email me. You can see a clip of HD video that I uploaded to Youtube from the follwoing link:
www.youtube.com/silcreation
Regards,
Manoj