So my understanding is that a lower-mileage cluster can be put on a higher mileage car, and you can synchronize to the higher mileage to remove the tamper dot.

You can put a lower mile cluster on a higher mileage car and keep the lower mileage, but that will keep the tamper dot.

So I'm still trying to figure out if I have a carfax issue or someone messed with the car - seems like a lot of work to get lower mileage without the tamper dot (keep in mind this discrepancy on carfax was 5 years ago). Plus why do it on a car that didn't have that high mileage to begin with?

I mean if it were a 200K car sure maybe worth rolling back. But rolling back 20K miles at 90K doesn't seem worth the effort (if it can even be done)