>Any ideas about why mail is running cpu at 100%?
Do you have any Mail Add-ons/extensions?
In Mail under the Window menu item>Connecxtion Doctor, does that show any hangups?
Not certain, but this can fix myriad Mail problems...
Safe Boot from the HD, (holding Shift key down at bootup), it will try to repair your Disk Directory while the spinning radian is happening, so let it go, run Disk Utility in Applications>Utilities, then highlight your drive, click on Repair Permissions, then move these folder & file to the Desktop.
Move this Folder to the Desktop...
/Users/YourUserName/Library/Caches/Mail/
Move this file to the Desktop...
/Users/YourUserName/Library/Mail/Envelope Index
Reboot.
If that doesn't do it and you can afford to redo all your Rules, try these & reboot...
/Users/YourUserName/Library/Mail/MessageRules.plist
/Users/YourUserName/Library/Mail/MessageRules.plist.backup
>if these are problems that will follow to the new machine???
Tough to tell, but I'd try MA at very first boot, easy enough to start over with a fresh install if so., but let's see if we can get Mail to quite down first.