Is it vapor locking?

I've had my Sunbird for 7 years, a few years ago it started acting up in the summer time. If I drive somewhere, get out of my car and then a little while later get in it and go somewhere, when I slow down to stop at a stop light it will sputter and die. If it dies I have to let it sit for about 20 mintues and it will start up just fine but will continue to do the same thing. Now if I put it in nuetral and then push on the gas and push it into drive it will go. OR if I'm driving on the highway (I used to work an hour away from where I live) and I can feel it sputtering, if I drive it long enough it will stop doing it. I've had it to a few mechanics and they've checked over pretty much everything but they never had any answers for me. We have a feeling it may be vapor locking, but if it is, we're not sure how to fix it. Can you help? Please?