It may be the case that if you cusotm built the PC, one of the components may be out of stock, so they're having to wait for more stock.
My Cougar PC arrived by Amtrak, and I was told what day it would arrive. I didn't bother tracking it, as it's a quick process. Amtrak have to take it to their central hub (wherever that is) and then send it out to you, so they'll have it for about 2 days before you get it. It turned up when I was told it would though.
A word of advice - I know their website says this, but make sure you write 'unchecked' on the delivery note. Amtrak managed to drop my PC and smash a lot of it and the lady at Amtrak wouldn't talk to me until I said I'd done this.