New to me low mileage ISX

[Rawze]

if your going to retrofit it with a dump box, your going to need a proper set of rears, like 4.11's, maybe 4.36's or even 4.86's if it is going to d a lot of local hauling. - ISX does not like being driven hard below 1500 rpm unless you are hell bent on shortening its lifespan.

as far as getting it running properly,.. pull the emissions cans and have em baked, flow tested and de-ashed. -- Whatever is in there is not going to come out by itself if it has really sat around that much.

EGR tune-up should be done too, and replace the IMAP sensor.

the entire DEF system, all hoses, the injector, tank, def filter, every part of that system is going to be problematic if you don;t flush/service it thoroughly.