AFAIK, not directly. For finding min/max you can use max-min function List::Util module on the array which you use for plotting.

use List::Util qw(max min sum);
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As for the labels. I thought you it's you who put them in

use GD::Graph::lines;
my $my_graph = new GD::Graph::lines();
$my_graph->set( 
               x_label => 'Label X',
               y_label => 'Label Y',
               title => 'Your Title');
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