If your pole building has that many leaks, running the trucks aint going to kill the mice, and its going to cost you a fortune in fuel. I'm not a cat fan, but sounds like you need a new cat, or a few of them.
I seen a movie one time where the barn was so overrun with mice that this farmer tossed a cat inside to kick mouse butt, but when he went back into the barn the following morning the cats was tied, strapped to a support beam and a group of mice had it surrounded and were throwing lit matches at a pile of hay they built up around the cat. I forget the name of the movie, "Willard Moves His Family To The Country" or something like that. Anyway, the farmer managed to save the cat and took a beating in doing so, but for the rest of the movie, the cat was never the same and wouldn't even come out of the broom closet it was hiding in.