04 f-150 fx4,when making a turn onto a side street either right or left, sometimes the steering becomes stiff and u pretty much have to force the wheels straight again, when i first happen i thought i had a flat front tire. all trie pressures a good, and my power steering pump makes no whining noise

 

Check the Tie Rod Ends (Inner and outer on each side)
Check the Idler Arm
Check the Pitman Arm
And grease any fittings you find.

That's what I would start with.

My quess is the Idler arm or Pitman arm are causing your trouble.