Still not sure what I was doing wrong the most as 1 shot would be fine and then the next terrible yet nothing had changed as far as lighting, distance, settings etc. it was weird. I have never fought my camera so much to get some consistency. I was shooting with manual Focus, as you say locked on the pack of cars and panning which I normally have no problem with but the Trucks themselves would only have to be slightly further back on the cars and I think I ran out of DOF because if I focused a bit more to the middle of the wreck I may get a good shot if the Truck stayed true but if it was slightly forward towards me then scrub the pic again. I think I should have just given up and watched as even a shot in the daylight when they were practicing came out shocking. I can go to a Moto X meet and take a 1000 shots over the day and be unlucky to have half a dozen out of focus.
Just one of those shoots you want to forget.