If your service calls are sometimes taking a very long time it may be a configuration issues with IIS. If the settings are not correct your IIS app pool could be recycling too oftern. You can view when IIS app pools get recycled by looking at the Window's Event Log. The recycle events will be recorded in the Windows Logs\System and they will tell you why the recycle was requested.
Here is an example of one of those log entries:
A worker process with process id of '10788' serving application pool 'Complex' has requested a recycle because it reached its virtual memory limit.