So non-Cosmetic vehicle slots. How many of them can be on at once?

[LectraWyraph]

There is another square on the Vehicle slot thing on the side of the left slots not appearance in order from left to right of... Utility Defense and Performance, and then a fourth slot which is faded out I don't know if that's another defense or performance or what.

Can vehicles only be given three upgrade slots, or is that fourth square there for a reason? Can there be two performance slots or defensive slots?

[ShadetheDruid]

One utility, one performance and one defense. And yes, you can only have one of each category/bonus.

Not sure what's up with that fourth greyed out slot, never even noticed it before. Unless it got added in the last patch. Wouldn't be surprised if it's been there the whole time and I just didn't notice though.