2001 Hyundai Accent while turning to the left it is a little harder

2001 Hyundai Accent mileage: 65,000. While turning to the right, the steering wheel is soft and effortless but while turning to the left it is a little harder (as compared to right). I checked the power steering and wheel alignment, and they are okay. What could be the problem? Due to this problem, the car tends to move to the right gradually while driving and you need to hold the steering wheel firmly so that it does not go to the right. At first, I thought it might be alignment and tire pressure problems. I even interchanged the front tires which have lessened the effect, but it is not gone 100%.