Rob -
I'm on my third 3.5 Ecoboost f-150. I bought one the first year they were offered (2011) then a 2017 and now have a 2023.
Never a single issue with any of the three. But, as you might imagine, I've not put more that 50,000 miles on the first two and now only have 12.600 on the 2023.
Given you have a 2013 I'd guess that you know what a beast the engine is. Those twin turbos really make such a large vehicle fly! However, I assume you also know that there are reports of serious engine problems with those early models that have over 100,000 miles on them.
The only other comment I have concerns the gas mileage - I had hoped for better MPG when towing (I get between 12 and 13 mpg on annual fishing trips from NC to the Rockies and back). Not towing I get 22 on the highway - 65 mph on rolling Interstates here in NC and more like 17 around town.
Each of the three I've owned have had the 6.5 bed because I ordered mine each time. I did ask about why the 5.5 seemed to be popular and was told that the foot shorter bed provided for easier driving around town and was about all most people needed to haul mulch and kid toys.
Bill