these two

If you do choose one of those two, get the one with the D13. D13 is pretty bullet proof.

 

I know I can't say anything specific about doing anything illegal BUT..... Since you ONLY run off road and NEVER drive on a public road...
Buy a 2011 or newer truck with any engine except a Paccar because you can delete DPF/DEF and EGR from any engine except a Paccar (Paccar uses EGR coolant to cool the turbo, you could put a single stage old style turbo on but thats too much money)). Financially you're better off spending $5,000 deleting that stuff from a newer truck instead of buying a 20 year old truck with 2 million miles on it and replacing every part over a 5 year period. Buy a $40K truck with 600K on it and spend the $5K getting rid of the problem stuff.

 

ISX you can get it fixed anywhere. Volvo pretty much stuck with them fixing it.

 

That's cause the isx break so often, need more places to fix it.

 

ecm programmed with incorrect tire size,diff ratio,etc. usually tire size.

 

IT all depends.

What are you going to haul?

ALSO as mentioned volvos are hard to find good service techs outside of the system while Cummins are easy to find.

BUT that said ...

IT all depends on the dyno report and the other testing to see which one is in good shape.

 

ECMs and odometers almost never match. Minor differences are not a cause for concern.

 

@ 500k miles many major parts are about to croak. The EGR system has probably been neglected and could be looking at needing new filters (around $6k for both DPF/DOC) ... The Cummins would be my choice... But if the EGR system has been neglected and not maintained there's a good chance the injecting cam will be pretty chewed up or on its way ... The VOLVO motor is one that many techs are not familiar with... If you get the ISX make sure to buy the big Amsoil filter part number bmk30 and plug it into the oil port by the oil filter and a return hose to the pan... With any EGR motor you have to fight back the soot the motor will produce... Let's see, the ISX has about 2 sensors that need to be changed yearly and the doser injector needs to be changed every two years, change the exhaust back pressure sensor ASAP, they go bad right around 500-600k.... Don't rush into these trucks... But if you must