I had the same problem and tracked it down to dry u-joints in the steering column.
I used a dental pick to lift the rubber seals on the u-joints and sprayed penetrant/lubricant into the joints and needle bearings, problem solved instantly for the cost of 8 shots of lubricant.
My truck steered very stiffly when the weather was below freezing and would steer normally when the temperature was warmer.
It was so stiff below 32F that it would not return to straight ahead when you let go of the wheel after a 90 degree turn.