MY APOLOGIES! I expected this was going to be fairly simple - "Oh, you forgot to do XYZ..." - Now that I read your replies, I wish I had done more before I posted.

• I will dig deeper tomorrow: removing the RD, measuring the alignment angles of the rear cassette relative to the chain rings, vertically and horizontally, use string to test overall alignment, check the alignment of L & R chain-stays to each other.

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The original post is below
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• The RD is a Shimano Deore XT M772 with long cage.
  • This is a NTB 9 speed RD, but the throw = 10-speed Shimano road system.
  • I've replacing an earlier version, the M771, and I've used that for over 5 years.
• The Ultegra shifters have not changed (except for a new cable).
• NO FD for now! But I do 96% of my riding on the middle chain ring so it's no big deal, and it removes one variable from the mix.
• The alignment of the frame, hanger, crank, etc. all seem perfect from any angle. The only things I've charged are the cable, the RD, and the chain.

I hope the picture is sufficient to explain better. I rotated the image 1° to correct the vertical alignment.

Is this a frame you cold set and you need to align the derailleur hanger after?

Two things, smallest cog is the high gear, so you adjust the H screw. Also, the cable may be stopping it and you will have to loosen the cable at the derailleur and allow for more. And, make sure you re-adjust the L screw so the derailleur doesn't go into the wheel.

John

I don't know what cold set means - the hanger is solidly mounted, aligns perfectly as far as I can tell...

Does the derailleur go far enough with the shift wire removed and the "H" (not "L") screw backed out?

To start loosen the cable clamp on the derailleur and if it shifts to the small thentthen cable was to tight.
if not adjust the limit screws. It's easy just watch how it moves as you turn the bolt.
A bit of trial and error will have it working.
But be very carefully you don't adjust it the wrong way so the derailleur can shift into the spokes. Double check when you are finished.
I usually shift it in to the low gear and then snug the limit screw up. And I also push on the derailleur hard to make sure it can't
Remember if it can shift into the spokes it eventually will and be a disaster so take your time.

Aligned perfectly by eye for 8 speed and up is just "not good enough" in the real world. You really should get the hanger aligned.

Does that need to done by a "big time" LBS?
Can I do it myself using precise straight edges, etc.?

Interesting Q - I will check it tomorrow...

One of the first methods to assess a situation is to separate the various elements from each other's influence and see how each sub unit functions. Andy