Trulia and Zillow are not updated as often as the MLS. When the agent puts it as pending in the MLS, it can take several days for it to show as pending in these sites.
Sometimes agents add their listings to these websites manually and if they don't remove them manually after the listings goes pending, then it takes a very long time for Trulia and Zillow to figure that out (if they ever do).
Are you working with an agent, your agent will do al the leg work for you. they will check the status on all the listings you are interested in before showing them to you.