Poor Performance on a table

Hi ,

    I have a table in my production database which has 500k rows and
from the pg_class it shows the number of "relpages" of
around 750K for this table, the same table copied to a test database
shows "relpages" as 35k. I run vacuumdb on the whole
database (not on the table individually but the whole database) daily.
I think because of this most of queries are slowing down which used to
run much faster before.
  Is there any way to fix this problem ?

Thanks!
Pallav