Use the burn tool on the shadows. For the chrome areas don’t use a soft edge (airbrush), chrome has hard reflections. Also, I know there are lots of pieces on this but you seem to put highlights and shadows (very thin) on some but not every piece so I would go through every single piece and do that. For the most part though it looks good, just needs the final touches. I think what you have going on in the seat/tank area is good so apply that everywhere.