As noted in the other post:
http://community.cartalk.com/posts/list/2116278.page
P1399 does seem to be a random misfire code - though a somewhat mysterious one as there is little concrete info on it. as noted in the other thread, though - if you do a web search on it you will find talk about it along with talk that it might be related to clogged egr ports. (your other thread said you replaced the egr valve, but did you thoroughly clean the ports to the manifold?)
btw: this is your 3rd thread (that I know of) - if you want people to help you the code info - along with any other info you have all needs to go into the same description. even with all of the information these problems are puzzles - but impossible if you scatter all the pieces in different boxes.