I wonder if there's excessive play at the steering wheel? Look at the intermediate shaft for 'possible' wear, freeplay. It only takes a micro-amount of 'play' between the steering wheel and the steering box to translate into a decent amount of steering wheel freeplay at the steering wheel ...which can be like a wondering condition. And there are like 4 joints in the intermediate shaft ..all which could contribute to a little excess play.
The easy way rule out the intermediate shaft is to have the tires pointing straight, and lightly clamp a vise grip pliers around the steering box shaft. Don't put it on so tight as to make 'marks' in the shaft. Then the handle of the vise grips down with string/rope or whatever using a block of wood against the frame/engine or whatever you have handy ...so the pliers is against something securely and it nor the shaft will move.
Then go inside the truck. With the steering column unlocked (engine off), rotate the steering wheel gently with your hand. You don't need to use much force. The steering wheel shouldn't really move. If there's wear at the U-joints you'll feel it in movement. If you do discover movement, have a helper gently rock the steering wheel while you inspect the joints to discover where any slop is coming from.