The thing about kings is that they have a huge appetite and tiny little heads. They tend to have to eat smaller food than other species of the same length and body girth. I have a cal king about that age too and he's just barely able to choke down rat pinks, he eats like 6 of them in one feeding but he couldn't eat anything bigger. Who knows, maybe the thing IS eating 8-10 pinkies a week. I'd want to have a look at it before deciding it's underfed. Anyhow, good luck, scoring a free snake is always cool.
I feel a little light headed... maybe you should drive...