Struggling to write a query letter and synopsis. Having the most ridiculous amount of trouble, no matter how many websites I read about how to write a good one.

What I want is a hotshot marketing person to do it for me! (But, as they say, 'I wants, never gets'.)
As for the synopsis, I'm currently working with the Snowflake method (very appropriate at this time of year) by Randy Ingermanson. He has a good way of doing a synopsis.
Maybe take some time off and come back to it. Often helps.