Looping pins 3 and 11 together did bump the output signal to 3.3V.
It was crazy — I have a system that’s supposed to trigger at 1.4V, and I could see the ~1.6V SH level going into it, and it just wasn’t triggering. If I slowed it down, it would sometimes trigger. Very odd. I hooked up a function generator and exactly matched the SH output signal, and it triggered perfectly!
So, something about the pull down and series resistor or amount of current available to source coupled with my digital IO card was causing more voltage loss inside the card. The bump to 3.3V in solved it all.
