select sql slow inside function

Hi,

I have a function proc_TaskComplete that inserts a record to table
TaskHistory and then calls another function proc_ExportTaskComplete,
that will retrieve (select) the record just inserted based on an index
column (TaskId) in that table TaskHistory. I noticed that the select
sql (inside proc_ExportTaskComplete) will take 3 seconds. Under normal
condition (psql) the select sql is fast enough with the index. Can
anyone explain why and how to fix the problem ?
My postgresql version is 8.4.4

Thanks,
Gary