ugh, I don't need cookies. That would ruin my running/biking regimen...
The next thing I would do is try and raise the float height by 1mm and see if that helps to keep the fuel level in the carbs a little higher. But don't do that until we have more opinions voiced on this subject. There are others here with more experience with carbs than I.
My reasoning on suggesting that is that if the deceleration is just enough to cause the fuel to not get delivered, and we know the petcock is delivering fuel, raising the level of the fuel in the carbs by 1mm might get continuous fuel delivery, even on deceleration. At least it wouldn't hurt anything to check the float height to be sure they're at the proper level.
Normally I would automatically suggest a carb cleaning for a bike having, but that doesn't seem to be the case here. (unless it's having trouble idling/starting/small throttle inputs?)