Second MIA and just realizing it's been months since I first posted this. But I wanted to say thanks for the help and if anyone finds themselves in the same predicament, my AC idle is gone!
So I realize this is long-winded, but I took a very indirect route in getting this sorted and kind of happened on it by chance. After finally getting a good TPS, I reset the computer and began racking up some miles in hopes of the truck relearning it's tables. Sadly, when the AC was on at full warm-up, (like a half hour of driving), the rough idle was still there. I don't regret the TPS as I've always suspected it of other things like a lag when flooring the truck, etc. Unfortunately, that's still there too, but driving with the new TPS is more than a placebo effect. It's not "wow" but more of running crap gas and filling up with Shell V-Power or something on the next tank. That sort of thing.
As for the truck, I swapped the factory radiator 6 years ago with a Spectre. At that time, I picked up a new thermostat, radiator cap, (20psi), and serpentine belt, (BANDO 6PK2605). Figuring this AC issue is likely not related to the cooling system but definitely begins to happen when the truck is fully warmed up
and the fact the coolant is 6 years old, (very low mileage in that time though), why not flush everything? Well, no matter how much love I show this thing, it just creates a million obstacles. When removing the Thermostat housing for the flush, I broke the inner bolt just underneath the throttle body. I wrestled forever but short of removing the intake plenum and hoping I could extract the thing, I decided on going all MacGyver. Before the "open eared design" that started in like 07 or so, the 06 t-stat housing has two ears that are held in by the two bolts. I took a step drill bit to the t-stat housing to create a recess where the bolt would normally go and, treating the now-broken bolt like a stud, secured it with a 6mm nylon locking nut and washer. Genius!
And I ran a flush. This is where the old truck just keeps testing me. There wasn't really a need to toss any product in there, but if you're changing and flushing the cooling, why not put in a bottle of flush I just happened to have on hand, (the Prestone one)? Emptied, added flush and water, drained, added distilled water, drained, added unopened coolant I didn't need 6 years ago, drained, and filled with new coolant. Good, right? Queue a meme of someone pulling your chair right before you sit down.
Finally - get to the solution man!
I noticed my coolant reservoir just about empty after each drive and a strong coolant smell in the engine. As usual, I couldn't find anything so I could only assume my make-shift solution to the T-stat housing was letting some coolant out and immediately burning it off. Fast forward and I broke down and bought one of those cooling system pressure test kits. I only pumped to 10psi and immediately there was coolant come out. I couldn't see exactly where, but it was behind the fan shroud. I'm betting running 6 years on 20psi again and tossing in a flush killed the Spectre unit. Time for another radiator change - this time going back to Motorcraft and adding the 16psi cap.
And unlike 6 years ago, since I have everything out, I pickup a new water pump (Motorcraft), 3 new idler pulleys, (Motorcraft & Gates), new Tensioner (Motorcraft),
and new serpentine belt, (Motorcraft JK61032AC). As I'm comparing the new and old parts, I immediately noticed the Bando belt from 6 years ago is maybe an inch bigger than the Motorcraft I just bought. But the new one is still a little stiff from packaging and maybe 6 years, even with low miles, put a little slack in the Bando. After I get everything installed and back together, the idle was immediate. Even without the AC engaged!!!
Somewhere between the tensioner and belt, (and maybe idler pulleys), the stock spec is back! I realize this is a long rant and of course, AC season is winding down now, but I just wanted to say thanks again and hopefully this helps someone experiencing the same issues or who is about to change a radiator and contemplating whether or not the "extra" stuff is worth it or not.