Stable release. It seems that once you hit 20 or so in a skill, it starts increasing at a crazy rate. I do use my car for clearing out towns of zombies, and also tend to drive through swarms of swamp critters at 200 km/h, which means I spend a fair amount of time repairing my car, but I’m up to 77 in mechanic now. You’d think that skill gain would get progressively slower and slower, and up to a point I think it does, but it seems that there is a hump somewhere, and after that it starts increasing really fast again.
I think you’re not supposed to go above 20 in a skill, that’s why it goes nuts.
Did you get to that level naturally or with debug?
No debugs of any kind, no mods, just playing the stable release. (For a long time.)