Those spec maps are most likely the reason. Spec maps in GTA V support RGB colors rather than just using greyscale, with each channel having their own effects such as shine or reflectivity.
I've attached the default spec map as an example. The tires are meant to be dark blue or purple. Light green or light blue is used by default for black or grey rims or hubcaps. Red affects the shine and green the reflections. If the color is brighter overall, the effect is stronger.
It's sometimes difficult to find colors that work well with the diffuse map. I would recommend trying something like R 150, G 100, B 150 in-game and continue adjusting it.
So here is the progress. The tires are better but not where they need to be. The rims have literally no change no matter what I do. I'm stumped there.
P.S. the tire part of the hubcap/rim texture is not used. The tires are a separate texture lol
It could be the polygon normals are messed up too. Doesn't seem like a simple spec error.
Did you recalculate the rim normals by any chance?
No I did not. I'm not 100% sure how to do that.