i'm having a similar issue that Joenaples was having, https://www.allfordmustangs.com/forum...ped-drive.html
'cept of course my car is a 2001 GT. i did recently have the transmission serviced but i've been noticing the vibration since before that.
the vibration seems to go away at just a few miles per hour instead of 10-15 like Joenaples mentioned, but that may not be significant. like him, i only notice the vibration in drive, but not park, reverse, nor neutral
it's been intermittent but seems to be happening more regularly now. when it happens, it will happen during the course of my trip until the car is shut off. if i'm lucky, the next time i start the car, the vibration doesn't happen.
my mechanic told me transmission mounts a while ago but i'm not sure if he knew it was an intermittent vibration. if it was the transmission mounts then wouldn't the vibration be happening all the time instead of intermittently, between trips? also if it were the mounts i would have expected the transmission shop to notice that and fix it? then again the transmission shop was extremely dishonest so they might have just ignored it.
maybe just placebo, but it also seems when the vibration isn't happening, the car drives/accelerates a lot better/smoother...