New Chain + Old Cassette = Skipping Chain???

Steve Sr. wrote:
Hello,

I just put a new chain on a drive train with a used cassette. The
combination is Shimano XTR 9-speed with an 11-34 cassette on a touring
road bike.

Since doing this I have noticed that the chain occasionally skips when
in the smallest 3 cogs. There doesn't seem to be any consistency about
when the skipping occurs. It seems to occur about as often while
standing and putting considerable force on the chain as when sitting
and putting minimal force on the chain.

If the cassette was worn I would expect it to skip more while standing
and not at all while seated. Is this logic correct? Anyody know what
is happening here?

Stiff link perhaps? (Or funky quick link?)

On the same vein is there a good way to measure the wear on the
smaller cogs of a cassette? How do you know when it is time to replace
a cassette?

My rule has always been when it skips with a new chain -- although only
experience with that has been on mountain bikes...and it's the BIGGER
(grannier?) cogs that wear out on me!

Bill "mtb pie plate" S.