Welcome to the club!
My fuel gauge also typically only goes to 7/8 as well. Apparently there is a recalibration that can be done, but probably only by a dealer and their specialized testing equipment. It doesn't bother me enough to drive over an hour to the nearest stealership to get it looked at. There's more here on the subject, just search away.
The vibration and clunk/thud typically point to a pooched front engine mount. KennyBoxster posted up an amazing DIY to replace a bad mount. Look here:
Boxster Motor Mount Tips & Pointers
+1 on the trans oil change. Once again, an easy DIY project.
Udo
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