ever had fuel tank over pressure and leak gas?? Help?

I just picked up a 180sx and the fuel tank always has alot of pressure in it when you open the gas cap. even if I open an hour later it has alot of pressure. and now it also starts to leak little drips from the tank when it´s all pressured up. If i let the pressure out it stops dripping. I tried replacing the gas cap, didn´t help. Oh, and it tends to leak after i have been driving around, and i park and turn car off. I haven´t noticed it leaking while running yet. Any ideas?
Please help!
Thanks

my sentra leaks fuel similar to that, if i tighten the cap all the way fuel leaks out of the evap canister, i just leave the cap cracked a bit, no problems

I am currently doing the same, but this actually alows evaporated gas to escape, which is very wasteful, so not a long term solution. There must be an answer.