In the pic it looks like the measurement is about 1.325"-1.350", are your cab mounts the original or have they been replaced? I just took a measurement of mine and it is just over 1.375" and the body lines look a little bit off as well, my dealer just replaced the C pillar cab mounts about a week ago but I never payed attention to the line before they were changed.
I took my truck in on the 29th of June and they informed me on the 2nd of July that they had ordered new mounts and they would be in the following day. I got a call late that Friday letting me know that they got them installed and the noise was still present, they asked for more time with the truck so I left it over the weekend.
I ended up picking the truck up the following Tuesday because they ran out of ideas and said they were gonna do some research and get back with me. I haven't heard anything back yet and will try to make some time to call them tomorrow to follow up. I wasn't given an invoice when I picked it up so I don't have part numbers for what they installed but the service manager told me that it ended in AE which he said indicates it has been superceeded four times starting with AA.
It seems as if the rattle is worse now than it was before they were replaced but I have only driven it a few times since I picked it up. I located a 2020 MegaCab at another dealer and visited them to test drive it, it had 5 miles on the odometer and rattled right out of the parking lot so they are still currently coming off the assenbly line with the issue.