'99 Grand Prix GT, 48,000 miles.

Dealer, several shops and many Internet resources have given me many
solutions as to what might be wrong, but no one knows for sure. I can't
find a shop even willing to troubleshoot this one. This has been
happening for almost a year. Any suggestions are appreciated:

My problems:

- Car shakes slightly at idle when engine is warm.
- Car sometimes gives off strong gas odor when starting when engine is
cold.
- Car starts and stalls or cranks, shakes and won't start after filling
up gas tank when engine is warm. Sometimes restarts within next couple
of attempts if I push the gas pedal down. Sometimes I have to wait
about 20 minutes, then the car starts (this is what happened to me a
few times after filling up). It'll crank but the entire car shakes and
pressing down on the gas doesn't do anything in this circumstance.
- On a few occasions the car stalled without filling up and it was
after I had been driving for a while, shut the car off and then tried
to restart it within a short period of time. The car then will not
start again for about 20 minutes. I can "almost" get the car to stall
after shutting it off and then restarting it after it has been driven a
while. The car will shake and then recover itself but still remain a
little bit shaky.
- Car does NOT stall after filling up gas tank when engine is cold. If
car has been off for many hours and I start it and drive the quick
under-a-mile or so just to get gas and not allow the car to get very
warmed up, I have no problem.
- Service Engine Soon light has never come on when problems occur.

Fuel pump and fuel filter changed. New gas cap. New spark plugs and
wires (routine maintenance). MotorVac carbon cleaning service performed
(which fixed another problem where my gas pedal was hard to press down,
presumably from a carboned up throttle body). No gas leaks. No trouble
codes set.

Somebody...help...  Shops will suggest problems but express uncertainty
how to fix it and say live with it. It's driving me nuts. Main
suggested problem is the Evap system. Anyone ever have similar problems
and if so how'd you fix it?