> Can anyone explain why this may be occurring and how I might be able to
> keep the original database running at the same speed as "tempdb"?
You're not vacuuming anywhere near often enough. Read up the database
maintenance section of the manual. Then, set up contrib/pg_autovacuum
to vacuum your database regularly, or make a cron job to run "vacuumdb
-a -z -q" once an hour, say.
You can fix for the case when you haven't been vacuuming enough by a
once off VACUUM FULL ANALYZE command, but this will lock tables
exclusively as it does its work.
Chris