Not trying to be a smart !@# trucer, but if a scanner is a bit expensive for you then I would stay away from buying a 6.0 for now. I bought a Scangauge II before I had even set my sights on any particular 6.0, but was pretty sure I was going with a 6.0. I'ts CHEAP insurance that you might, at the very least, catch something odd on your test drive.
You will know things like FICM voltage, your ICP and IRP values, and the biggie in my book is the delta, or temp spread, of your EOT(oil temp) and your ECT(coolant temp).......should be 15 degrees or less on a 15 minute test drive going at least 60 on a good stretch of road.

Knowledge is power. The truck I bought was an '03 bought up by the Twin Cities, and things looked good to me on the test drive and on the way home with my car in tow on a car caddy.
The HPOP went out two weeks later, but with the help of this forum and some savvy members, youtube vids and local knowledge I was able to get her back up and running myself.
I got bit by the 6.0 bug like so many others here, but don't go into a purchase like this without at the very least a way to check some things out. It's not worth saving $150 only to find out later you have problems that amount to what might be thousands of dollars, simply because you wanted a particular truck.
If nothing else, if something is iffy, you have some bargaining power at the dealer as an educated buyer who knows a thing or two about that engine. I would insist that you see the 3k worth of repairs that were done, might have been things that were not all related to the engine.
Don't ever take somebodies word that previous maint was "good".........that is a pretty broad brush used in the truck world.

 

Most of the stuff you need to know is in this thread from the Tech Folder. Lots of other good stuff in there also.

https://www.ford-trucks.com/forums/9...used-6-0l.html