2008 F-150 4x4 STX Power Steering Issues
 

Need some help with a power steering issue I just started experiencing.

1. I have had loss of power steering intermittently. While driving and sitting still turning wheel, while engine running of course.
2. If making a right or left turn while driving, the power steering will come and go as I make the turn
3. I thought it was stuck in 4WD (auto engage switch on dash) as we have been using 4wd often this winter, but that doesn't seem to be the case, think I have ruled this out
4. Seems worse in cold weather.
5. All fluids are good, and no whining noise coming from pump
6. While driving at highway speeds, if I need to change lanes left or right, the steering is difficult, and almost dangerous.
7. While driving and making a right or left turn, the steering will not assist and help return to center (don't know if I am explaining it correctly, but steering is almost sticking)

Does this indicate the Power Steering pump may be going or is bad? What about the rack and pinion?
Any suggestions on helping diagnose the issue would be helpful.

It sounds like you have an issue with your rack & pinion and possibly the steering wheel shaft universal joints between the firewall and the rack itself. Either of these will present the issues you have described. If the P/S has never been flushed I would try that first and put in some additives to help re-lubricate things.