Day 91 for my Navy Federal CashRewards comes up on Thursday. So I decided to call and ask in advance about the 91/3 CLI. I was told point blank, "Let me tell you, when requesting a credit limit increase from Navy Federal it will absolutely result in a hard pull. The possibility of a soft pull does not exist."
This has been posted many times before:
A CLI request will almost always be a SOFT pull if you wait 91+ days from issue, with 3 statements issued and on odd-numbered months (jan,mar,apr,jul, etc) after your NFCU online FICO score has updated (AR). As an example, if the card was approved in May, you want to request a CLI after the first week of September 2018. In your case, since your 91 days was after the odd month (May) AR, I would suggest you wait for the next AR which would be July.
No matter what the CSR told you on the phone there are many many examples of successful "soft pull" credit limit increases posted on MyFico using this method - including both my DW's cards and mine.