Could you also post a higher resolution version and the donor(s)/reference(s) used?
There's some jaggy lines, which could be from resizing or from using wrong feather on the pen tool. If that's it you should set it to around 0,2 or use the blur tool to soften the edges.
The red parts of the wheels look a bit saturated and it's obvious the center cap is colour changed

Certain area's like the front and roof look like they could use more detailed work to it.
Overall it does look impressive but details are hard to comment on with the size of the image.