First make sure you are monitoring the system called "Palmetto (Project 25)" and not the City's system.
If that still doesn't work, try removing the Six Mile site from the scan list and see if that helps as the city is on the simulcast site and not Six Mile. Since scanners have trouble monitoring digital simulcast sites, it will constantly jump to Six Mile (or one of the other non-simulcast sites). I've heard there have been some issues with adding/removing sites from multi-site trunked systems on the PSR-800, but I don't know enough about the radio to tell you how to do it.