Awhile ago a federal TRS with the Sys ID of 3517 (which is in the RR DB) was thought to be used by both the USPS and Customs and to located in NYC and at Newark IAP.
Is this still the case?
You are correct about the US Postal Service (Postal Police & Inspectors) utilizing the Federal TRS in Manhattan. US Customs (i.e. CBP and/or ICE) does not utilize this system, they are still on their VHF Conventional systems.