I've gone up pretty steep things with mine (5-spd, case doubler, 6.6:1 in dual low) and never had an issue.

Are you hard on the throttle when it does this? Potential for some wiring issue when the multiplied torque shoves the drivetrain around more than normal?

And it did this at a decent RPM? Probably less of an issue with an auto trans and tq converter, but I've occasionally stalled mine (before I had the doubler). And they don't like restarting when they die under a load like that, I guess there's extra fuel still in the intake.

At 3/4 tank, it's unlikely to be a fuel supply issue, at least in terms of the fuel pump sucking air.

I'm sure there was a lot of distraction in the moment (to say the least) but did the dash lights do anything weird you can recall? Any OBD2 codes stored (they might not set a CEL)?