At 46K you are approaching the cost of a new leftover model (2014) that some dealer would like to get out of his inventory!
The 6.4 is way over priced give the problems that come with many of them.
With either one I would buy a service contract from the selling dealership!
Remember many feel the 7.3 was the last good Ford diesel!
"Both trucks were bought and sold back to the original ford dealer where bought new. They both have all service records."
You sure that we were not bought back because of issues. Ask for a Ford Oasis Warranty service report on them.
Note also the Ford tends to blame fuel issues with the 6.7/CP4.2 on the user, while GM with the same injection pump quietly covers CP4.2 problems. I failed pump repair is 10-11K!
Chris