This seems to be a data structure described in the C language. Most likely, you will want to build a string using pack (or rather unpack) to decode the information from the GPS device. From reading the description, the following pack template might be what you want:

my $template = 'vvV';

read $client, my $sync_packet, 8
    or die "Couldn't read from client: $!";

my ($syncHeader, $syncID, $unitID) = unpack $template, $sync_packet;

...
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