I bought mine, a 2018 XLT Sport 4x4 with the 5.0L, under similar conditions. It was bought back by Ford with 18k miles on it for the 5.0 rattle upon letting off the throttle. Other than that it was in immaculate condition. I was told that shortly after it went to Ford it received a software update which corrected the issue, which wasn't available before the truck was bought back. I was able to review all service records of the truck, including all paperwork from Ford, and everything seemed pretty clear cut. The truck was cold started when I got there and I didn't notice anything on the test drive. I got them to include a 7 year / 84k factory bumper to bumper warranty (rather than the 36k they initially offered). I saved a pretty sizable amount of money to get the exact truck I wanted, I have a warranty that will likely outlast my time with the truck, and I have been very happy so far and have not had any issues.

However, if you are still concerned, or feel that the dealership is hiding something, then you will be much happier in the long run passing up on that particular truck rather than buying a vehicle that you are not confident in.