Don't know if anyone has come across this game for PC but it's called "Spin Tires". It's still in beta and you can download the developers version and add different vehicles and maps etc.
It's not a bad little game, you can engage 4wd and use diff locks and get bogged etc, i'm currently using a GQ comp truck.
SPIN TIRES LINK
MODS LINK
I'm having fun with it as is my son.