Here are some tips for tunning ur cobol + db2 program
1) In the sql's used check out if the column names in where clauses have indexes, if not check out if an index can be created.
2) Try to avoid joins, if not able to avoid try to have them on keys.
3) Sort the i/p data accordingly that for the same i/p u dont hit the database again and again.
4) Thru DB2MON check if a particular querry is taking extra ordinarilly more time.
These are some of the means...
As far as testing u can use expeditor.