2003 Kenworth, w/cm570, crate engine in 2016

[Irishflyer97]

I am looking at a 03' Kenworth with a 400ST crate engine, about 250k on that. I'm assuming any updates where done by then? I'm new to the ISX, and getting hopeful reading this forum that the problems they did have can be managed. I am curious about what areas to inspect. I will insist on a valve cover removal, but after that kinda in the dark. Another question, rather subjective, but what sort of fuel mileage pulling a grain hopper could one hope for with a pre-egr ISX, with an APU?

Thanks!