Try something like this to use the stream option instead of trying to interpret CIM etc...

$IPConfig = get-netIPConfiguration | Out-String -Stream
ForEach($item in $IPConfig) {
            If($item.ToString() -like '*DefaultGateway*') {
                    $defaultGateway = $item.Replace('IPv4DefaultGateway   : ', '')

            }
       }

write-host $defaultGateway