My 98 civic EX has this weird problem

I start the car (at any time whether its cold or not) and begin to
drive.  After about 30 seconds the car starts to shudder or hesitate,
as if it is suffocating or not getting enough fuel.

It is most noticeable with my foot just lightly pressing gas, if I
floor it the problem quickly goes away until I shut off the car again
and re-start it.

It happens every time I restart the car, as If theres air in the gas
line which enters the injectors at some point causing this problem.

The check engine light came on, and I had it scanned for this reading
Code: P1457 EVAP leak.

What could it be? Does anyone know this code?

I think it could be a control valve or something near the gas tank...
almost like the valve is not fully closing when i shut off the car
allowing air to enter the line?  Does this sound right?

Ive read somewhere that this problem can be caused when you over fill
the gas tank, which i have done a few times since buying this car in
august 07, though I don't overfill it anymore.

One other thing I have noticed with my car, only when the car is cold
that when I release the clutch going into first the car shutters a lot
no matter how slow or easy I pull out the clutch.  I have also noticed
that sometimes shifting from first to second or second to third I
think my clutch is slipping (doesn't do it all the time though).  Like
it keeps reving sometimes even with the clutch fully out. Could this
be my friction plate going?  Or may it be tied to the above problem?

Thanks for all your help in advance!