Cover letter reads as machine written and the careers office picked it up in two seconds

Not a research question, sorry. This one is for me. Applying for internships over the break and I have sent 14. 2 replies. The careers advisor read two of the letters and said both times that she could tell, and when I asked her what gave it away she said the rhythm, which I do not know what to do with. What I have tried. Telling it to write like a human, which does nothing at all. Giving it three of my own emails as style examples, which holds for about a paragraph and then it goes back to whatever it was doing. Asking it to avoid the obvious words, which just moves it on to the next set of obvious words. There is a detection paper I read for something else (Gehrmann et al 2019, or it might be the DetectGPT one [ref]) where the signal is that the token choices are too likely, and if that is the same thing then asking it politely for variety was never going to fix anything. Although I might be joining two unrelated results there [check this]. 2/14 is not a rate I can improve by guessing at it. Adding this ten hours later, since it is the middle of the night where most of you are. Wrote one myself first and asked it only for cuts, no rewriting, and the advisor said that one was fine. So possibly the answer is to not let it write. That is not an answer to what I asked. Due Sunday either way.