My Box only fills to 3/4 gas tank
 

I've been having this problem for a while, that my gas tank only fills to around 3/4 tank. Then when I force the gas in, it overflows, so I know it's filling up. And when I get back in the car, the meter doesn't go past 3/4 tank.

Any idea what the problem is?

It somewhat common in Boxster to get the gauge stuck. Some people have a gauge that reads 1/2 full, anywhere in between a full tank and 1/2 tank. Then below the 1/2 tank mark, the gauge begins to work and read to true amount. In your case the gauge is not moving past 3/4.
You can probably get it fixed, but I would just do the OBC hack then you will always have a very accurate reading, and it only costs about $50 to do.
:cheers:

Do a search on the performance discussion for "fuel gauge". I just fixed this same problem last week. It's not too tough, but you need to be careful around the plastic bits.