Power Steering very heavy - tried everything
 

Hi all, I have a bit of a head scratcher for you all, hoping someone has some bright ideas....

I have a 2007 Audi A4 2.0T Quattro Cabrio with 190000k on it. I have had it 3 years and since i bought it the steering has been very heavy. It's almost as if the steering resistance is fixed at a particular level and does not get lighter at low speeds. I honestly do not notice any change in resistance as I drive it.

Here is what I have done to try fix that so far to no avail
1 - replaced the steering rack with salvaged rack immediately after i bought it. This fixed a knocking problem but ZERO impact on the stiffness of the power steering
2 - replaced all tires and did wheel alignment - no difference
3 - replaced power steering pump with OEM salvage part - PS fluid flush - ZERO difference
4 - replaced power steering pump with a quality new German after market pump - PS fluid flush - replace with Audi PS fluid - ZERO difference
5 - mechanic inspected steering column no issues found

What is confusing me the most is the following (hopefully this may spark something) about 20 months ago during a really hot summer's day (i guess between my steps 2 & 3 or possibly between 3 & 4 above) the car was sitting in the sun all morning. I took it for a drive and WOW the steering was perfect, super light and easy to turn, a real pleasure. Then later that same day it returned to it's normal heavy self and it has never shown that lightness again. That is the killer here, I know what it should feel like now and I can't get it to come back.

Does anyone have any outside the box ideas for what might be my issue here?

Thanks in advance