One thing I think you need to do is get some high level coaching/lessons to work on various parts of your game.
I took 5 lessons from a great pro and after my lesson yesterday, he remarked that I had made a huge improvement from the first one 6 weeks ago. I changed my serve, my backhand improved, my volleying was much more solid and my fitness improved considerably. I've never been more confident in my game and had some recent wins over 4.5's that I never would have beat even a couple of months ago.
A "3.5" backhand isn't going to improve by just playing, you need to revamp it completely. If you're really serious, you need to be an open book and soak up some knowledge from pros. The key is to find a good pro that will help.