A little constructive criticism-I hope you don't mind. If the truck on the right had been cropped to the size of the two trucks on the left, I think this would work better. But that's just my opinion. It's your work.
Ok, I see what George is saying... but what I see is the truck on the left is taller than the other two with the one on the right being the lowest... there is a symmetry there. Love your triptychs, yiannis!! Great subject!