You can unofficially register your Challenger at http://www.dodgechallengerregistry.com/index.php. By holding the cursor over the status code on the chart, you can find out what each code means. "D" means "Firm Schedule - dealer has allocation and all parts available. It's ready to go on the assembly line.
(I look at the "order progress" like a UPS tracking number - the status reflected on the sight may not be totally accurate......it could actually be further along the line than indicated in the tracker.)

Sorry - I have no idea what the "priority code" signifies.