Yep, those gradients are vectors to project the textures in data/textures/cars to the 'psuedo-3D' chassis. It's worth noting that some of the textures are made up of two parts, a main colour layer, and a mask layer. For example, here's 'MyClub.ktx' combined with its mask - it's completely transparent and might be worth noting:
applecuckoo - ripper of sounds, sprites and models
Places to get help:
DYKG/VG Resource Discord - This is where most of the ripping experts on the VG Resource hang out these days, so you should probably start here. Any requests to rip stuff (i.e. "Please rip sounds/models/sprites from game X!") are only allowed here as per the rules.
ResHax forum - Another forum that is home to most of the reverse engineers who were on the old ZenHax and XenTax forums. A great place to get help for any mysterious files. I'm also there under the same username.
And remember, always upload example files. That way, people don't have to dig in and fetch them for you.