Bad performance on table access - how to analyze?

Hi experts,

I am new on Sybase ASE with a just a bit of experience.

We have the problem, that on accessing table COEP we have a very very bad performance since a few days.

The days before it was good with the same read-logic.

We have one index including mandt, objnr and TIMESTMP.

We read with mandt and objnr.

If I analyze with st12 I also can see that the index is used.

I've already checked statistics and did rebuild the index.

however performance is still very very bad.

Does anybody know, what I can do next?

COEP is very big, around 95 MIO entries.

I tried index-check in dbacockpit, but got a connection timeout.

Thx for any ideas.

Kind regards