I send packages to the USA fairly regularly using NZ Post International Courier.

 

Usually the tracking system is pretty good, but I recently had a case where a package was showing "In transit with airline" for 4 days (it doesn't take 4 days to fly from AK to LA). Of course I feared the worst.

 

On advice from a US forum, I went to the USPS tracking page (NZ Post hands over to USPS) and registered for tracking updates.

 

Within minutes, I received an e-mail stating that the package was being processed by Customs. Whew! Crisis averted :)