I think you have found the pertinent diagnosis and fix.  s

I had the same problem, performed this fix, and it didn't really do squat.
The problem was air in my lines.  The pulsating (shudder) is air in your
fluid compressing with every pass of the pump impeller.  There is another
service bulletin covering this, and the special tool you need to buy to get
the air out.  Have fun.  This hydraulic system is a POS and it took me
several tries to get all the air out, even after purging and replacing the
old fluid (which you'll also want to do..).  2-3 dealer techs I talked to
said it's very rarely the pump or rack.

D

It was time for new tires anyway, so we had that done on Friday.  Amazingly,
the shudder in the steering stopped.  So at a minimum I can say that the
tires were a large contributor to the problem, and by getting new tires, the
other factors aren't enough to cause the problem.

Not a cheap fix, but something we had to get done before winter anyway.

Thanks for the previous replies.  I'll hand onto them in case the shudder
returns.

Craig