ROB: I actually got to sleep in a bed last night, after spending Sunday night on the floor of the hospital, and now my head is clearer regarding Tosafos. If you read Tosafos and the Gemorra he is explaining which says one who removes oil from a lamp is chayav kibuyi, it is clear he does NOT consider removing fuel grama. Rather Tosafos is rejecting the option that the kibuyi is merely causing the fire to burn less time, say there was oil for 4 hours and now only enough for 3 remains, because if that was the only issue it would be grama. Therefore Tosafos explains that when removing oil it IMEDIATELY causes the fire to become smaller, which is true kibuyi. Certainly the same applies with turning off the gas, and even Tosafos would consider this kibuyi mamash. The Rosh disagrees and considers removing fuel to be true kibuyi even if the flame is not affected instantly, merely it will burn less time. This is because the oil is already “connected” to the fire even if it is in a separate container. This would certainly apply to gas as well. While I understand your difficulty with Rashi and the Rosh’s logic, I don’t think we can change the Halacha based on that.
Re Rashi: I think the simplest explanation for Rashi is that we are talking about a kli with holes on the sides or suspended in the air above the fire in a manner that will not cause the fire to be diminished at all but will insulate the beam from its heat. Why do you assume it will go out at all when Rashi seems to indicate otherwise?
Re grama in general: One of the main sources for grama is the case of removing a dam from a river where effect of the initial flow is considered your direct action and the continuation is grama. Reb Shlomo Zalmam Auerbach considers 5 seconds to be certainly a delayed reaction, hence many of the Grama innovation he pioneered for medical uses.