[68c10airstream]

As you drive in the heat the return line brings warmed up fuel back to the tank and the tank gets steadily warmer. I also suspect poor quality fuel pump as they can cavitate because of the poor quality especially with warm fuel. Although not the key item for your issue be sure the throttle body is clean, (helps with good idle), replace the air filter if you hold it up to the sun and can't see daylight through it and clean the mass air flow meter (maf). Look up in this forum as how to do it. When the maf is dirty usually it runs rich at low idle and lean during high rpm's. Air filter and the throttle body cleaning doesn't cost much.

With the engine shut off, take the vacuum line off the pressure regulator and check for wetness at the vacuum/regulator fitting. Any wetness means replacement.