Well since I seem to be in a similar boat, I will share my thoughts and experiences and maybe some questions.
So I have the big radiator, 19"x34" core. I have Windstar fans mounted to this radiator controlled by the Sniper. The larger fan comes on at 180F, off at 170F so it stays on most all the time. The smaller fan is on at 185F and off at 175F. (I adjust these temps up 5 degrees in the winter FWIW) The interesting thing is the Windstar fans only cover an area of 17"x28". So there is a lot of radiator without fan coverage. In front of the radiator I have the biggest B&M stack plate transmission cooler I could get that has its own fan. I do not have AC.
On the last trip my engine was overheating on any kind of hill climb, both highway and on the trail. I would push it up to 220F and then stop to cool down. It would cool down within about 15 minutes. On the highway my speeds would stay at 35-40mph pulling the camper up the hills which I feel is enough speed to be pushing more air through than the fans can pull. On flat ground with the camper in tow running 65mph the temps would stay at around 195F. This is with outside temps of 90-95F. And this was all towing the camper. I only drove a little on the highway this weekend without the camper and the truck was still heating up on hill climbs just not as quickly as with the camper.
So I think I could solve the trail overheating with bigger fans and shrouding the entire radiator. I'm just at a loss for the highway cooling. I should be maximizing the air flow through a pretty large radiator and it still doesn't keep up. I wanted to add AC, but then it would really be struggling.
I too have thought about moving the trans cooler away from the radiator.
@muddysub did this in his burb and I think it has been working well for him. My trans temps are not going out of control like the engine, which I'm happy about. I just don't want it to become a problem by messing with things.
It's interesting you are having the idle cooling issues because one of my other next step ideas was to install a mechanical fan and shroud. I was worried the idle/trail temps would become a problem and based on your experience that could very well happen.
I did notice in my searching and looking at factory 454 fan components there apparently was a factory electric fan that would be installed on the AC condenser. So maybe not surprising that you're using an electric pusher fan with your mechanical fan setup.
I'm also thinking I want to try adding an engine oil cooler but again this will need to be mounted somewhere other than in front of the radiator.
I didn't have this trouble for the first year I had the Holley Sniper setup on the motor, my troubles began with the 4l80e install. So I bet your problem is probably coming from the addition of AC and not from the FiTech.
Don't know if my post is of any help, but thought maybe we could at least compare notes and commiserate.
