What LowCel says about learning to carrying speed is a very good point. If you can, try to pick up an occasional training partner who is also a downhiller (provided they are decent at XC too
). In trying to keep up, you will learn the little things about how to carry more speed through corners, rollers, rough sections, etc. It might give you a totally different way of looking at how to attack technical sections.
I know this because, when I go on XC trail rides on my hardtail, there are many places where I find I'm coasting more and maintaining the same speed as the other riders in the group who are pedalling much more than I am.
Good luck. It really sounds like you're doing very well; be patient with your progress and proud of how far you've come.