Question for Blacksnapon

[Tennesseepowerstroke]

I got the water to run clear after flushing twice with VC9, countless gallons of tap water and over 100 gallons of distilled water. All of this after 20,000 miles and 4 years of running the yellow gold. Strange to me, my deltas are 7 to 12 cruising at 65 mph with the cruise set. When I cruise at 65 and run at wide open throttle [25 pounds of boost] my deltas always drop to 3 or 4 degrees. Anyone care to comment on this?

I wanted to go with Rotella Ultra ELC but am afraid to until after I change the thermostat, for fear of the EOT getting too high.