I have an inclination why you may be struggling with the D300s. When I started off in photography I owned a trusty D40, my first year speaking honestly, well I never really grasped any of the technical side of things, it was my compositions which I consider to be my strongest point seemed to pull me through and somehow I just winged it (shot in auto most the time, when I did venture away from auto the results were pretty dire!). A mate of mine at the time had a D200 which I had on a couple of occasions was lucky enough to have a play with. It confused the hell out of me, why? Because I never really grasped my D40 to begin with. It was not even so much the D40, it was the very fact that I did not understand how iso, aperture, shutter speed all impact each other and how to use each of them to compliment the other. Equally, the first time I was passed a Canon to have a play with, again completely stumped as did not understand it. Now its a completely different matter, I shoot in full manual all the time (and generally get my exposures pretty good) and understand how each setting (iso, aperture, shutter speed) impacts each other, so can pick up any camera now and the only thing I need to know is where on the camera each of these settings is, everything else, completely irrelevant.
It does very much sound like you are incredibly wrapped up with having the best kit, or just professional kit, you've actually forgotten all about why you are interested in photography! I think what you need to do (as already has been said), is to stop buying equipment and focus on what you do have (which is much better than what I own, I might add) and actually use the camera. Learn how to take a good shot, learn how ISO, Aperture and Shutter impact each other.
Whilst I don't condone any of the off the cuff remarks towards you, I equally am starting to realise why you get jumped on every time you post. Coming practically last in the comp every month, yet raising thread after thread about purchasing expensive kit (sometimes talking about the next next upgrade, when you have only just got your current one), obviously you are going to have a lot of people scratching their heads.
I'm no expert at all, but would always be happy to help. Perhaps act as your critique before you submit into the comp?
