Ryan leech's the art of trials is really good, good fundamentalsfor mtb.
the brianlopes/lee mccormack book is good.
fluidride was a good dvd, lars sternberg looks exactly the same 10+ years later.
dirtschool by resetfilms was basic but good.
They helped a lot, as did some skills coaching with bernat guardia (dh wc rider) a few years ago.
http://betterride.net/ this had good advice.
those dvds can be found on youtube, they're only as good as the time you put into practicing them.
There's a really good race bmx school here, I'd like to sign up as soon as I've got some free time.
might be an idea to look for some coaching. it's a mental thing, or sorting out details, that really take it to a different level.