it's not running parallel like i thought it would. If it takes about 4 sec to create/save a customer record, it's taking 20 seconds for it to run 5 promises, or if i run it:

var cust1 = createCustomer('promisd', 'testing', '', '<mailto:promisedtesting@nautilus.com|promisedtesting@nautilus.com>');
      var cust2 = createCustomer('promisdd', 'testing', '', '<mailto:promiseddtesting@nautilus.com|promiseddtesting@nautilus.com>');
      var cust3 = createCustomer('promisddd', 'testing', '', '<mailto:promisedddtesting@nautilus.com|promisedddtesting@nautilus.com>');
      var cust4 = createCustomer('promisddd', 'testing', '', '<mailto:promiseddddtesting@nautilus.com|promiseddddtesting@nautilus.com>');

      Promise.all([cust1, cust2, cust3, cust4]).then((values)=>{
        log.debug({title: 'promise all', details: values});
        log.debug({title: 'promise all', details: `${Date.now()-startTime} ms`});
      });

it still takes ~16 sec for it to run, so either i'm doing it wrong, or netsuite isn't allowing it

Hey well you saved me some time because I've been wanting to run similar tests. Even if they don't run async, I still think there's a structural/maintenance benefit to using them. Nesting callbacks can get nasty.