Will not start hot - sometimes

I have a 2002 Grand Prix GT and during real hot weather, it will sometimes not restart after I shut it off for a few minutes. First started happening when on a trip (> 1 hr. driving at higher speeds and hot weather) and stopped for gas. After fueling, it would not immediately retart (it would crank). Waited a few minutes, then it would restart.

The last time this happened, I sprayed ether in the air intake and it fired up for a minute, so I think it has something to do with fuel delivery. It's getting worse now, but it will always restart if left to cool off long enough.

Anyone know what this could be? Two trips to the dealer and they could not duplicate, nor fix.

Thanks,
Earl