Personally I don't get the external oil cooler thing. It's a solution in search of a problem. The problem is sludge/silicates from the Ford Gold coolant and leftover casting sand.
The solution is switching to an ELC rated coolant and installing a coolant filter. I'd do that first and monitor vitals. That's $200 instead of $2000. The OEM cooler is up to the job. Just my opinion. If I towed heavy trailers across Death Valley I might reconsider.
2005 E350 RB 6.0 PSD for extended fun
1989 Landcruiser FJ62 for local fun
2011 VW TDI Golf for hwy fun
FYI - Not sure if still listed on eBay, but for at least the last 2 months someone was selling a new BPD oil cooler for Econoline (new in box). If memory serves, believe he was asking around $1,700...if itís still listed he may take less since itís been on there for a while.
I totally understand on the coolant quality issue and have installed a coolant filter on my 6.0.
Fortunately my oil cooler is operating very efficiently as it currently stands (usually within a couple of degrees). I just don't like the idea of hot coolant cooling my hot oil and the consequences of the two coming together. In saying that, there's no way I'd spend anything close to $1500 to instal a air-oil cooler. I usually fabricate anything along those lines myself.
I would like to see my Engine run slightly cooler at higher speeds. Leaning towards fabricating some hood vents for that purpose.
Start monitoring your transmission fluid temps. Trans fluid runs through a heat exchanger in the radiator so all three systems are linked. The transmission cooler in the vans is very small and if that's over heating, it can cause your coolant temps to spike.