Q: Why can't I read/write from/to a 25LC640?

The code I have works fine with a 25C320

I am specifically using a 25C320-/P and 25LC640-I/P.
I am running at 5V so both should respond at 3MHZ.
Just like the MicroChip specs say they should; the
64K 640 should be a plug in replacement for the 32K 320.

The Microchip FAE says it should work.  Even though
the Microchip specs for the 640 are still "Preliminary."

What gives?  What could I be missing?  Did they forget
to mention something about the 640?  The docs look like
edited 320 docs.

The timing is as the docs spec.  Checked with a logic
analyzer.  And yes there is 5ms between writes.  Yes
the /CS line toggles.

A new Tribal programmer is coming at the end of the
week (too long a wait) so I can check to see if we don't
have a tube of bad parts.  But, I don't think they all could
be bad.

I need fresh thoughts!

TIA,
Walt.....