Hey 2-70's, I am dealing with something like this on my '65 with a 5.0. Did you ever figure it out?
Mine was running great and then one morning the car started fine and the idle raced up and down until it finally settled down to normal. I could drive it with the occasional stall and once warmed up would idle normally. I replaced the ECT sensor and it seemed to help for a while but over a period of weeks it got progressively worse. I replaced the IAC with no change and now it won't idle even when warmed up and stalls like yours was doing.
1965 Coupe 5.0 GT40 Intake and Heads, 65MM TB, chipped, T5, Shelby drop, roller idler, subframe connectors, Magnaflows, Hurst shifter, MS clutch, BFGs on 15" TTDs, Roller perches, Bilsteins, 3.54 gears, LS, Needs everything else...
"If you didn't build it; it's not really yours."