Help needed on camera purchase.

Hi, I am a transport photographer and I need help on my next camera purchase.

As most of my photography is done from bridges or roadside, a lot of my photos are of fast moving vehicles. My current camera (Nikon D3200) is failing to live up to expectations. I've tried using many different settings but the photos either come out to dark, to light or blurry.

As my knowledge of cameras and the numbers (ISO etc) is pretty poor, I was hoping someone would be able to steer me in the right direction of a camera that provides good quality results in all sorts of conditions (sunny days, cloudy days).

I was looking at a Nikon D7000 but as I've mentioned, my knowledge is pretty poor of cameras!

Many Thanks, ChrisM92