Here are the Best Practices and Troubleshooting articles which are related to GUP.
Group Update Provider: Sizing and Scaling Guidelines
Best Practices with Symantec Endpoint Protection (SEP) Group Update Providers (GUP)
Configuring the Group Update Provider (GUP) in Symantec Endpoint Protection 11.0 RU5
Guide to create the GUP for remote location
How to Setup a Group Update Provider (GUP)
Tips For Installing SEP In A Low Bandwidth Environment
Symantec Endpoint Protection (SEP) Group Update Providers (GUPs) Selection
Troubleshooting the Group Update Provider (GUP) in Symantec Endpoint Protection (SEP)
How can we check which content SEP 12.1 clients are downloading from GUP?
How to confirm if SEP Clients are receiving LiveUpdate content from Group Update Providers (GUPs)
SEP Content Distribution Monitor (for GUP health-checking)
How to analyze Debug logs from GUP to determine which clients are taking definitions from GUP
Video’s created on Group Update Provider on the Symantec Connect website.
GUP content monitoring tool video
Hope it can help to all.