I'm with you, that sure sounds like a lot of food. I fed my 38 chickens when I had all those roos, about 1-1/2 gallons of food only in the evening time. They free ranged most days and I think that was even a bit much on feed with them free ranging.How long have you been feeding the FF? The amount you are feeding is staggering, so I'm doubting you are not feeding enough but I'm wondering how long they've been on the FF now and if it's had time to flesh them out with a better type of nutrients.
And on a side note...chickens will always act like their throats have been cut when it comes to food and I've noticed that has increased exponentially with the FF, but I doubt very seriously if it's due to hunger, as my own flock are waddling like geese on only 1.5 c. of FF per day for 13 full grown, standard chickens.