I would go for the Dodge because of the Cummins engine. It was designed as a much heavier duty engine than the Ford (Navistar) engine and will give many more miles and years of service.

I personnaly would go after a later 90' truck with the inline (P7100) Bosch injection pump. This pump was designed for heavy duty line haul applications. It can handle the new lower sulfur diesel fuels with no issue (engine oil lubricated pump cam). The VE disrtibutor pump is fuel lubricated and has problems with low lubricity fuels.

I was Chief Enigneer on the Cummins B series engine (used in the Dodge ram)for a period of time and have seen engines returned from the field for evaluation with more than 900,000 miles. The oil consumption was measured and found to be at the "new" production engine specification.

Good luck on your search!