Before the cooler I was seeing 160-175 on flat ground with no load, towing the trailer on grade I hit 198.5 on my monitor which while "safe" was a bit high for my liking.
Now with the Derale in place I see 150-155 on flat ground no load, and saw no higher than 182 on grade and that was just briefly it was averaging 175 on grade with the trailer which is right where I'm comfortable. I don't have a fan on my cooler, but have it same as yours radiator to derale to transmission. The truck still currently has the engine mounted fan but I'll be removing that and adding electric fans in the near future.