95 G20 5.7L – Runs rough on second start

This van runs great when first started and continues to run fine until it’s turned off and restarted. When first started vacuum at idle is steady at 21” and 10” at 55mph cruising speed. After parking for 10 to 20 minutes and restarting idle is still steady at 21” vacuum but the van hesitates on acceleration and runs rough at cruise with a 5” vacuum. If I continue to drive I get low vacuum trouble codes for the MAP and Oxygen sensors (http://viglink.pgpartner.com/mrdr.php?url=http%3A%2F%2Fviglink.pgpartner.com%2F search.php%2Fform_keyword%3Do2%2Bsensor&mode=). I’ve replaced the oxygen sensor and performed a diagnostic on the MAP sensor which checks out ok. I’ve checked for vacuum leaks – none found. Does anyone have a suggestion on what to look at next?

Tank fuel pump was at 6psi, replace pump now fuel line pressure is up to spec of 12psi. Van is back to running great!!!!!!!