I also suffer from GERD and no heartburn.
For as long as i can remember i had a chronic cough, (my 'normal' cough), and had 4 really ugly episodes in the past 5 years where i thought i was having a bad cold and it was all because of GERD instead. 3 weeks of constant dry cough, sore throat, ear pain, headaches... awful.
I am now 15 days post-op and feeling wonderful! I did 6 months of PPI'S and diet before surgery and it seemed to help a lot as well.
So far no coughing, no acid taste in my mouth, no pain... nothing. I am amazed with the results. I'm already thinking i'm one of the lucky patients with a successful Nissen =)
Good luck with your surgery! Make sure you read a lot about what to eat afterwards. It's very important in your recovery process.