If you noticed a substantial increase in oil/coolant temps after a flush, then there is a good possibility that your flush caused some combination of silicates/rust/sand to plug your oil cooler which will foul the effectiveness of your coolant system. If you were previously using Ford's crap Gold coolant, its likely that silicate gel was the main culprit. The only way to clear that is with using 'Restore' (not Restore Plus) during a flush. If you cooler is overly plugged, the Restore won't be able to clear the small oil cooler passages and you should then try a backflush. There are aftermarket backflush fittings that can be bolted onto a plate that sits above the oil cooler - access is through the doghouse. The one from Accurate Diesel looks like the best choice for a van engine as its slimmer and shouldn't require anything else to be moved.
Sorry if this is repeating the obvious, as I'm new to your site and don't know the history yet of previous discussions- I'm normally on Ford Truck Enthusiasts forum, but van's with 6.0's are few and far between there. They do have more info on the 6.0 that most other groups though, and tons of stuff on oil coolers and coolant.
Ford should be chastised for still recommending its 'Gold' when its well documented that any 6.0 that is run hard/hot (which is unavoidable with RV rigs such as mine) will experience silicate drop-out and subsequent serious issues. You are wise to be only using an EC-1 rated coolant, and brand type doesn't much matter.
2006 E-450, 6.0, 27' C-Class RV: hood vents, coolant filter, pyro gauge, ScanGauge II, Fumoto valves,