The other day I had to put brakes on real hard and swerve to the right.Now when i turn either way the steering seems to lock and all of a sudden it pops back it also does it sometimes going strait. It is a 95 f150 4x4.Going straight down the road it wants to go to right at times and holding steering wheel to left all of a sudden it goes back to the left.Sitting still moving wheel back and forth seems fine.

 

Can you turn from lock to lock (full left/full right) smoothly while at a stop? May need to be sitting in dirt or gravel for it to go smoothly. That might clue you in on the pump operation. If you can feel it popping while stationary, have a helper turn the wheel so you can see if anything fishy is visible when it happens.