the old adage of buying early gets the best price is long gone with DL -- if this trip is next winter, I would wait until mid summer, if not sept/oct to buy the tickets, if necessary. I would watch it and you should see prices on the other flights come more in line.
What is the fare now?
+10000
That used to be the case but now it is more like: Outside 90 days = never low and inside 20 days = never Low. I find the best prices seem to be between 20 and 45 days out.