First the gearbox:
As has been mentioned this is a small GTL bug.
Each gear option in the gearbox file is assigned a number in order starting with 0 so for example if you have a gear file with 15 different ratio options then they are numbered 0 to 14. These numbers are used to assign the ratios to the set up.
The Scirocco only has 6 options (there are 2 first gear options) so 0 to 5.
So as an example if you load a set up from a car with lots of gear options it might have choice #4 saved as 2nd gear so the Scirocco assigns choice 4 as 2nd gear but then there is only 1 more ratio choice (choice #5) left to fill the other 3 options so it makes all of them the same gear.
On the rear wing:
As mentioned above it is possible to modify the garage to show front and rear wing adjustment like in GTR-2
For this to work with a car it would need to also have a front and rear wing adjustment range assigned in its .HDC file
In the case of the Rocco they do not have any rear wing numbers at all so even if the garage were modified to offer the adjustment it would do nothing.
The cars do have some down force assigned to the front spoiler but there is no adjustment range assigned so any adjustment with a modified garage would also do nothing.
However many mod cars in GTL do have an adjustment range assigned to the front and rear down force settings so if you did have the garage option mod you would be able to add or subtract down force from them.
This would of course need to be considered as cheating if you were using this in any online racing.
On the disappearing wheels at a distance:
This is controlled by the load in and load out settings for the wheels in the .cas file.
In fact most of the parts on the car have these settings I believe. Markus could explain better than me.
Many cars have the load in setting closer than some of the far camera shots on some tracks. So the wheels don’t “load in” until the car gets closer.
I believe this is done to help conserve frame rates so your game is not drawing parts out in the distance that you cant see anyway but there my be other reasons that I am not aware of.