[ShadeTreeJack]

My 1998 Malibu starts and runs good. I hear a misfire but doesn't set a code. When it was 103 degrees last week, the car drove fine. I stopped for a few minutes then it would not start. soon it started but stalled and would not start until it had a chance to cool. it has been hot out everyday since then and I have the problem every time I drive it. most times it sets a P0341 DTC along the way, but usually can keep driving. Then It 'skips' like it going to quit, then goes for a few more seconds, then dies. The I need to open the hood and wait 45 minutes.Now every time I drive it, I need to open the hood or let it sit for an hour.
If I don't stop, I can keep driving.

I have replaced the Cam Position sensor. cleaned and added fresh thermal grease. swapped the ICM from the old engine(long story), swapped the coil packs from same. checked and moved the crank postiion sensor harness away from the exhaust - it was touching. moved the plugwires away from the CPS harness. cleaned the IAC and intake, MAF.
I have same fuel pressure when it wont start as when iot does: 40-42 psi. I have no spark when it wont start. I replaced the Crank sensor last year when I replaced the engine. I have a basic scanner and can read a few parameters. tps, and maf, map all seem to be working OK.

based on all the things replaced/swapped what could this be?

I replaced the head gaskets about two months ago. it was running great. Now it runs great, but has that slight misfire when idling.