In the same vane as tybalt89's example. A bit slower but maybe less obscure:

use List::Util qw( max );

my %hashName = (a => 1, b => 2, c => 3, d => 3);

my $mx = max values %hashName;
say "$_ => $hashName{$_}" for sort grep { $hashName{$_} == $mx } keys 
+%hashName;
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