This may seem like a grindy achievement but its fairly easy.
Once you win a season in each of the 3 categories, then just simulate every race from season 4 onwards, its only takes about 10mins to simulate each season as you still need to repair parts on the car every 3-5 races.
Just make sure you simulate in the Sprintcar category until you earn the $5 million dollar achievement, and if you still need to do any seasons after that just use the Midget category as it only has 14 races.
Good luck with it.
EDIT: I have been informed by TeslaMotorsMan that repairing your car isn't necessary as he got the achievement without doing it thus saving you a little bit of time.