First thing to do is to seperate the gas guage problem from the vibration problem..
For the vibration I would get to speed and put it in neutral to see if the vibs lessened..
I would go fast to see if they stopped..
I would apply the brakes slightly to see if they stopped..
Vibs at certain speeds can lead to out of round tires or bad tire balance.
Is the vibration in the engine itself? Running the engine up slowly while parked should tell this..
Is the vibration in front or rear? The steering wheel shaking usually means the front..Not shalking usually means the rear..
For the guage I'd fill the tank when 1/2 was showing to see if it truly WAS 1/2 tank..
Big JIm <img src="/forums/images/graemlins/pfft.gif" alt="" />