There's a lot of things this might be. First, try the obvious...

* "update statistics medium" for all databases.

If this has no effect on performance, try running some of the sqls in dbaccess, with "set explain on;" beforehand - output goes to a file called sqexplain.out - and should hopefully give you hints as to which queries are slow (anything that is "SEQUENTIAL SCAN" is bad - might hint at a missing index).