2012 kia sorento mk2 diesel, 4 cyl 2.2L
Hydraulic power steering
The power steering becomes very stiff every 10 seconds, left or right. Although mostly right hand turns.
I replaced :
1. Power steering rack
2. Power steering pump
3. Front right hand side CV joint drive shaft (using brand new part)
4. Replaced with brand new steering fluid
Using 2nd hand parts.
The problem is still happening every 20 degree turn or ever 5 or 10 seconds the steering becomes very stiff and then becomes normal again.
Happens even worse when the car has been switched off and cold and just switched on and driving.
Using 2nd hand parts.
Some or all of those parts could be as bad as the ones you replaced. You might want to check output pressure of the pump to see if it's within specification.
The problem is still happening every 20 degree turn or ever 5 or 10 seconds the steering becomes very stiff and then becomes normal again.
Check to see if there's a universal joint in the steering shaft that's become stiff due to lack of lubrication.
Happens even worse when the car has been switched off and cold and just switched on and driving.
"Morning sickness" can be a symptom of internal steering rack leakage.
Using 2nd hand parts.
That's most likely your problem, it's a 14-year-old Kia. They made them cheaply. Scavenging parts off of similarly old Kias sold for scrap at salvage yards, especially Kias that are the same or similar to yours is one heck of a recipe for pulling your hair out. As @chucktobias says, make sure the pump is within spec at all times. If the pump doesn't maintain pressure, replace it with an OEM pump from RockAuto or something similar. Purchase a brand new one.
There is no fluid leaks found.