I had a pulling problem on my 02 V6, since it bought it with 63,000 miles. It pulled to the left at any speed. Coincidentally i put on new tires when i bought the car, some cheapo chinese brand, it was a deal with the car so i took the tires they gave me. Michelins they are not. But the car had not pulled on the test drive and now it did.

So lately i balanced these tires (fortunately i work in an auto shop). This left wheel was way out of balance so i fixed it. Then i moved the left front to the right front. Problem solved, no more pulling.

So if your car pulls, first suspect the tires. I had this same problem long ago with my 83 Sentra. And a mechanic at work explained to me how having different tires on the front, or wrong tires that the car "doesnt like" can make the car pull. He was right, the problem disappeared when i rotated the tires. So now that is the first thing i check if the car pulls.