The Kent School District has always had one of the better transportation departments in WA state.
I would be surprised if your bus has an AT540 transmission. I would be inclined to think it would have the MT640 transmission. Kent usually up spe'c'ed their buses. And I would be really surprised if Kent didn't spe'c auxiliary transmission cooler for that bus as well.
In every respect, it would appear as if you have found a pretty nice bus.
Good luck and happy trails!