why is it that on some records, sound terrible??

Here is the checklist that I run through in my mind whenever I install a cartridge, of things that need to be adjusted or at least considered:

Overhang.
Offset angle.
Azimuth.
VTA.
Tracking force.
Anti-skating force.
Load resistance (i.e., preamp input impedance).
Load capacitance.

It seems to me that any of the first six items on this list could account for the symptoms you are hearing, if not properly set.

Regards,
-- Al

Inner groove runs slower - it is not as good - it is not called LP = Long Play for nothing - some compromises were involved in getting LP to work. When I collected vinyl my favorites where the 12" 45 RPM - better sound - more dynamics and better channel separation.

Of course the slow groove speed at the end of an LP doesn't help, but in my experience the accumulation of dust on the stylus (as suggested by Mapman) is the culprit. It doesn't take much.

YES after playing one of the records over again and keeping the stylus nice and clean, the record sounded stable (better).

Cool!

Another pointless upgrade avoided!