dies randomly at idle in gear

[Boog]

My truck sometimes just dies while idleing in gear, even with the A/C off. It starts right back up easily. There are no stored codes. No obvious vacuum leaks.
This 91 sportside I recently bought is 350/auto and I have been replacing some parts I am sure are at least 25 years old. A little tuneup at the actual 82,300 miles.
I rebuilt the tb (nice conical spray pattern now), replaced the AC plugs and AC plug wires, fuel filter, ecm's coolant temp sensor with an AC one also, new thermostat.
About those plugs. The underhood label calls for plug gap of 35 thousandths. I gapped the new ones at that and it did not want to run, at all. I have never gapped plugs at 35 on an HEI vehicle, always 45. But I opened them up on this truck to 45 and it runs better. And the random dieing was happening before I began this tuneup.
The truck has been in the local chevy dealer's shop numerous times before I bought it for this and a trans leak they had trouble stopping.
I don't do business with that dealership.