Don't get me started on replacement radiators......
I'm not surprised your hoses are still good. That stuff doesn't wear out like they used to. And that lower hose is a huge PITA.
Transmission cooler: go big or go home!
Transmission cooler meant for the 6.0l diesel using the 4r100 transmission. I have a part number around somewhere but I lost about 6 months worth of data that was supposed to be backed up to the "cloud", so it'll take some digging.
As far as monitoring transmission temps, the OBDII reader will read the temps in the valve body (lower left corner of the digital gauge) and now rarely gets over 150 with the huge cooler- it would get over 215 in the summer around town (not towing) with the factory auxiliary cooler. The Autometer gauge I have is reading the temp as it comes back into the transmission from that huge cooler (it rarely registers a temp- and if it does, it goes down once I get moving).
I would assume that you have 3.55 gears- based on that I have 3.55 gears and a 2000 EB 5.4 with the towing package (just like you). I think XLTs got the 3.73 as an option.
How's your battery?