I am going to be replacing the radiator on my 03 8.1L Yukon XL soon and I have looked at this too. While searching I found this post on another forum.

I installed the new thin core radiator. I stopped by the local Performance Radiator store and asked about the thin core and was given a technical description of why the new thinner core was better. It has a denser fin design. The data said 4% cooling improvement over the thick factory core. The staff at Perf Rad said they have had no issues with the thin ones.

well I have 2 long trips, one of 1500 miles to Colorado up to high elevation and 4lo situations, and another of 1000 miles into Mexico deserts at 110 deg F. And the truck stayed cool, with no issues at all. I want to say it runs as cool as it ever did brand new.

I really was surprised that with a core almost 1" less thick and lower volume of coolant, it really works fine.

 

Wow, thank you for the information. I have been looking around but had not run into that post.

I ordered the AC Delco thin radiator, but unfortunately it came damaged and I need to return it. I sincerely hope the cooling performance is better as I have already overheated my transmission towing over some of these Colorado passes. I think I'll upsize the transmission cooler while I'm at it.

 

I'm planning on doing the Trucool and aux fan route for the transmission cooler like in Drakito's post. One thing I may play around with is the fan itself. The stock on one mine is pretty pathetic looking. I will look into if a 9 blade 6.0L gas fan blade will bolt in. I went from a 5 blade metal fan on my Jeep to a 9 blade off a Chevy Astro and that made a tremendous cooling difference.