could be..
Yeah,it could be the pick up coil in the distributor causing that..--it could be a wire connection somewhere heating up and breaking the connection intermittently too..bad ignition switch,or coil might do it too.(less likely though).you'll have to see if its losing spark right after it stalls..it might be the ignition module inside the distributor too,they can crap out intermittently too--
Sometimes they cause it to lose spark,sometimes it still has spark,but the part of it that fires the fuel injectors craps out..and they don't set any "codes" either,and can test "good" at autozone on their tester--then crap out after its back in the truck awhile later..they do this quite often--never "fully" die,but will let it start and run only somtimes,when it feels like it!..

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A genuine GM module is best,but costs a lot more than a cheapie at a parts store ..its a gamble as to whether that will cure it..a pick up coil can do the same exact thing..we often change both at the same time at my friends shop,rather than risk a "comeback"..sometimes he just swaps a rebuilt distributor in,its faster and easier than changing a pick up coil..(not exactly an easy job if you've never done one before-)and sometimes the shafts dont come out of the distributor easy,if at all)....
I don't know much about EFI,but I do know the IAC motor should only affect the motor at idle..and no,I doubt very much any exhaust leak at the header collectors have anything to do with it at all..you'll have to determine if its losing spark,the pulse to fire the injectors,or fuel itself...sounds like you've already covered the fuel system pretty well..i'd start looking at the ignition !..good luck...
