Hi i'm not an expert on A/T coz i'm also a newbi. But here something i can share with you. D4 is always use if you drive only * city limits and highway, while D3 is use if you are climbing on a mountain terrain area contniously. While 2 is being use if you tow another car or slippery road during heavy rain on a muddy area. When you park your car, always put the transmission stick on a P-position and every time you change the stick position you deep step the brake while shifting from one postion to the other smoothly. Hope this will help you understand a little bout automatic transmission.