Q: Why would my steering only be stiff when driving but be fine when I'm still or going real slow 2001 Nissan Frontier

The steering system is designed to have a hard steering at high speeds to prevent any rollovers. The Dynamic Stability Control or Traction Control is designed to keep the vehicle from over steering when driven at a higher speed. You can disable the Dynamic Stability Control, but I caution you for a possible rollover condition. When disabling the system, it would restore the full input from the steering wheel during any turn. If you need further assistance with your steering system, then seek out a professional, such as one from Your Mechanic, to help you.

Hello. It sounds like the pressure relief valve in your power steering pump may be failing. When this occurs the high pressure at higher speeds will cause this. If it has variable steering then the problem may actually be electrical.You should get some assistance from a certified mechanic, like one from YourMechanic, that can come to you to [diagnose why the steering is so hard] https://www.yourmechanic.com/services/steering-wheel-is-hard-to-turn-inspection