USPS is so slow right now due to major network overhauls by Postmaster General Louis Dejoy's Plan of "Delivering for America" where he focuses on ground transportation and consolidating of facilities, which disrupts the old systems.
This is also combined shortages of staff, reduced overtime and higher than normal mail volumes, like during holidays also creates bottlenecks, especially at new regional centers, and slows delivery and causes packages and mail to sit longer in the USPS sorting facilities.
The reason why your USPS package says moving through network, is because your package is actively traveling between USPS sorting facilities on a truck or plane and is en route to it's destination.
However your USPS package may not get another scan until the package has reached the next major USPS sorting facility or your local post office.
Delays for USPS packages can be a result of distance, batch processing and large volumes.
The USPS moving through network status indicates that the package is in the USPS system, but not at a final stop yet and delays can occur due to high package volume, weather or even mis-sorting of packages, although it's usually normal for USPS tracking to pause for awhile before updating again.
Your package being in transit to the next facility for so long can be a result of high shipping volumes like on Holidays and sales, as well as busy sorting facilities, long travel times, which could be on trucks or even temporary scanning issues.
If your package is farther away it can stay in transit for a few days or so until it reaches the destination sorting facility and some packages go a longer route, before it reaches your destination.
I wouldn't worry if the package doesn't update and stays in transit to the next facility unless it's been longer than 3 days to 4 days.
When the sorting facilities have a lot more packages to deal with, it can take longer for the packages to be sorted and scanned and sometimes the package may have arrived at the sorting facility even when it says in transit to the next facility, but it may not have been removed from the truck and scanned and sorted.
Moving through network USPS takes between 1 to 3 days depending on how far the package has to travel.
In most cases a package that is moving through network will take 1 day to 2 days, but for some packages that have to travel farther or during peak shipping times like the holidays the moving through network could take over 3 days.
In transit does not mean you'll get it today as in transit means that the package is on a truck and going down the highway or in an airplane traveling to the next sorting facility or to your local post office.
Once the package arrives at your local post office and is ready for delivery the USPS tracking will update to say arrived at post office and then out for delivery.
After the USPS tracking says out for delivery then it means that you will get the package that day.
USPS tracking is very accurate in most cases.
However there can be some delays in the USPS tracking updates.
When tracking a USPS package, the tracking only updates once they are scanned so it can take awhile for the USPS tracking to update and show where it's at.
Once the package leaves a post office, the package will get a scan indicating it has left the post office, then once it gets to a sorting facility, the package will then be scanned again and say it's at a sorting facility.
Once the package gets ready to leave the USPS sorting facility again it will say that the package has departed the sorting facility and will update to say that it's in transit to the next facility.
After your package has reached a sorting facility that is near to your address, then it will say arrived at a USPS destination facility.
Then once the package gets to your local post office and is ready to be delivered it will say arrived at post office and then out for delivery.
Finally once the package has been delivered, the USPS tracking will say out for delivery.
It can take 3 to 7 days for some packages to reach your address depending on how far away the package is.