OAuth 1.0 Signature Generation

I was provided a sample Postman collection from NetSuite for their REST web services. I am able to authentication and use the sample calls. I need to know what Postman uses, exactly, to create the oauth_signature. I tried the realm, consumer key, token key, nonce, and timestamp in my own integration but the signature comes out differently (when I have the same nonce and timestamp hardcoded in Postman and my integration). Help will be GREATLY appreciated since my forehead is quite flat from the banging against the wall.