If it were me, I'd use the unsolicited evidence form on the USCIS website to upload newer copies of tax transcripts to both, new marriage evidence to both, etc. Adding evidence can trigger someone to look at it, and it also sets you up well to then informally ask your local representatives to message USCIS on your behalf and ask what's up. You're taking a while; but not THAT long outside normal processing; so make the officer's job a little easier with some obvious evidence of a good relationship and give it a nudge.
If you've had any encounters with the law, and especially any abuse complaints, you're going to be waiting a while and will want to engage a lawyer.
Last, no, there's no reason to re-file a new 5-year N400 now. They couldn't approve it until they handled the I-751, either.