Tom
I did a side-side comparison some months ago. I just remember thinking..."yuk, everything is changed" Perhaps it looked worse than it was, but it seemed to me substructure was all redesigned. Even the tranny line routing was lowered, to a new low mount TOC.
If anything, all these nose changes/redesign did was make the fan more effective. Having listened to the LBZ folks, these fans run annoyingly like the LLY, even empty. I know this is a culture that has become accustomed to "you hear the fan and it's good news".
Nonsense. These are my experiences so far.
GM forgot to address inherent airflow in the redesign. They merely needed to design in lower pressure under body, and the problem would have been reduced to tolerable nuisance calls, IMO. The LLY (and LBZ) stack suffer from lousy throughput, the fraction of ambient air that makes it through the stack, at a given speed. It's 12% (of driving speed) with no fan. At 70 mph, there is around 10 mph flow.
The LLY towing envelope increases dramatically, just by adding a mod that moves a greater fraction through the stack at speed. Fingers demonstrated this a year ago with an air dam. While not pretty, he made a good discovery. The current stack and aero combination is underutilized. There is lots more heat exchange available just by getting more air through. Ambient air shortage is choking heat exchange at all times. But it only shows through under max demand, and high OAT's.
IOW, there is no "cause". We run out of heat exchange capacity. There are a few measures that I have found, that improve cooling system function. Some cheap, some expensive. The part retrofit, looks to me to be expensive and impractical, since it does not address what I want to address, ridding the fan. Ridding it completely, except at low speeds. It is errosive to economy, a nuisance to my eardrum, polluting, and just plain power sucking. I don't want a fan that works better, louder, and bigger. I don't want a fan that gets me to the next stoplight. People look at this thing in horror. The HP it consumes in a city drive, could power a house easily. The added pollution, just due to fan ops, is substantial. There all kinds of reasons to not improve it, IMO. I truly feel that GM missed the mark, even in their best attempt. It may take longer to overheat the LBZ, but they didn't fix the (main) deficiency. Cooling air shortage
IMO
All heat to be removed, must be absorbed by the air. The limitation in this issue, is the regulated temp of the coolant. At best, air can only heat up to the coolant inlet temp, about 200 degrees. Once air is at 200 degrees, it has no more heat capacity to carry more, so ect rises. (the only problem with ect rise, is that the system behavior begins to change also, especially pressure sensitive coolant properties) Adding airflow, allows more air mass to carry away more heat at this temperature.
This is the premise of my conclusions 2 years ago, and to this day, I have found nothing to controvert it. A few other improvements to be had, outside of airflow improvements include
A mechanism to remove entrained gasses (if present)
Added heat removal capacity, in the form of oil cooling
Coolant change to 30-40% G-05 HOAT, with a front thermostat change
Tuning-EFI has the best possibilities here, IMO
Improving IAT with a good (not aftermarket) CAI. A power draining thermal feedback loop exists in the stocker.
EPA equipment removal/modification-these are controversial, as they require breaking the law.
note: Different coolants have different properties, G-05 (a hybrid organic acid coolant) is the only one I have used and tested, so there may be others. GM tends to get upset at us for taking these things into our own hands, just be aware, they consider anything but dex-cool to be a warranty exclusion. Which I find interesting, since that position is in direct violation of the Magn Moss Warranty Act (law), which requires them to supply it for free, if they are to take this stand.
One of the most interesting discussions we had on another unmentioned site was the affects of +Pressure and -Pressure on airflow to/thru the stack. There was a small handful of guys that really understood this and took the time to educate the rest of us, very much appreciated. 
