Hmm. Bumping up my driving stats was a real pain. I had to restart the game with all the gangs resurrected (to give me some to mow down), but I’d wiped out all of Los Muertos and most of the Volk before I managed the 4 star rating. That gave me four stars for everything, though.
Then, I set about getting some of the achievements for stunts in cars, managing a few of them by taking an SUV up the lift in one of the Shai Gen buildings and jumping off the roof. Ace!