So taking your suggestions above, I have updated my scipt as seen below and this does seem to resolve my memory issue - MUCH APPRECIATED!

my $running : shared = 0;

###THREADED###
##Parse Fetch and execute DELETE
while (@row = $sth->fetchrow_array )
{
    ##Create and Run threads
    ##Limit running threads
    sleep 2 while $running >= $maxThreads;
    threads->create (\&deleteDevice, @row)->detach;
}

##Thread cleanup
sleep 1 while $running > 0;



sub deleteDevice($)
{
    ++$running;
    my $deviceSN = shift;
    my $full_url = "https://$api_creds\@$cwm_url$deviceSN";
    &debug("CMD: $full_url");

    #my $threadCount = scalar threads->list(threads::running);
    print "Current Thread Count: $running\r";

    # Get current subscriber info
    my $ua = LWP::UserAgent->new(
            ssl_opts => { verify_hostname => 0, SSL_verify_mode => 0x0
+0 }
    );
    $ua->agent("Device Deletion");
    
    my $req = HTTP::Request->new(DELETE => $full_url);
    $req->content_type('application/x-www-form-urlencoded');

    my $res = $ua->request($req);
    if($res->is_success)
    {
        &logDeviceDetails("$deviceSN -- Delete Successful");
                        
    }
    else
    {
        &logDeviceDetails("$deviceSN -- Delete Failed: " . $res->statu
+s_line . " - " . $res->content)

    }
    --$running;

}
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