From my experience there is push the week before the holiday and ford ships a bunch of cars (railroad never stops). Then when they start back up there a little "quality hold" (a day or two) to make sure everything is running smooth on the line. Even during the "quality hold" the run the line full bore and store the vehicles on the lot while inspecting. And after the hold there is a lot of product being loaded as long as there are empty railcars.
To answer your question there is a year end push, and first week of the year push. (7 years experience at forx mixing center, I always dreaded this time of the year)
lol I know whats going to happen. Mine will be one of the 1st off the line come 2012, and one of the first shoved in the corner of the holding lot. THey'll produce a crap load of trucks, fill the lot, have that quality hold for a day or two clogging the lot all up, then start shipping them out, and mine will be stuck there extra long since it'll be in the corner and not able to get out till the rest clears out LOL