Viscous couplings are supposed...
Viscous couplings are supposed to reduce parasitic power loss by allowing the fan to free-wheel when coolant temperature is below a predetermined level. They seem to work much better in theory than in practice; removing it added a full mile per gallon to our test vehicle's fuel economy.
Installation of an electric fan is not particularly difficult; removal of the original fan is a different story. The fan/coupling assembly mounts to the water pump pulley by way of a large nut that's virtually impossible to remove without the tool specially designed for the purpose. A 36mm open end (or adjustable) wrench and a big hammer will get the job done, but you'll save yourself a good bit of aggravation, and your knuckles a good bit of skin, if you buy or borrow the proper tool. After the fan is out of the way, the lower fan shroud can be removed and the electric fan assembly set in place. Since we used a "universal" type Spal dual-fan assembly, we had to fabricate the brackets required to mount it to the radiator support. The term "fabrication" is a bit of an over-statement-nothing more exotic than a few pieces of 1-inch wide aluminum, a vise and a drill are required to get the job done.
Setting up the fan's switch-on and switch-off temperatures using Spal's fan controller could be called "programming", but that would be another over-statement. All you have to do is press the "high" and "low" buttons on the controller when coolant temperature reaches the desired level and "programming" is completed. Unfortunately, the temperature sensor included with our controller was not of the proper metric persuasion required for installation in an LSx cylinder head, so we had to find one with the proper thread dimensions (available through most GM dealers, and many parts stores). If you can't find or don't particularly care about using a "genuine GM" sensor, BWD Automotive part number WT5132 is a suitable replacement.
Although single electric fans...
Although single electric fans are available, a dual-fan assembly is preferable for high engine-load applications like towing. This Spal dual 12-inch fan assembly is a "universal" type, so installation requires the fabrication of mounting brackets. They're bolted to existing threaded holes in the radiator support, formerly used to attach the upper fan shroud.
A more direct route to increasing an engine's power output is to improve its breathing capability. That's easily accomplished through exhaust system modification. It's truly ironic that auto manufacturers spend so much time and money developing whisper-quiet exhaust systems, yet installation of aftermarket systems with a significantly more aggressive sound continues to be one of the most commonly made modifications. Although many aftermarket systems are installed in the quest for a "deep, throaty exhaust note," such systems also deliver increased power. That's largely because the same characteristics that restrict sound also restrict flow; within limits, increased flow capacity equates with increased power output.
Personal preferences vary greatly with respect to exhaust system configuration, so there are many "right" ways to modify a stock system. (Don't consider that statement as a license to do whatever is quick and easy-some modifications are just wrong.) The advantage of installing a complete exhaust system is that cutting and welding are not required. The disadvantage is expense. The original equipment systems used on 5.3-liter GM trucks incorporate mandrel bent 75mm tubing, so there's little to be gained by replacing pipes-it's the muffler that constitutes the major flow restriction. Aside from being large enough to house a small family, the stock muffler has enough internal twists and turns to confuse a seasoned navigator. That obviously creates a good deal of exhaust restriction-and that can be eliminated by replacing the stock muffler with a low restriction model.
Spal's fan controller incorporates...
Spal's fan controller incorporates pulse width modulation, so it varies fan speed according to coolant temperature. "Programming" the controller is simply a matter of depressing the "high" and "low" buttons when coolant temperature reaches the desired levels.
Original equipment catalytic converters are another known power-reducing restriction. (The conditions under which a catalytic converter can be replaced are defined by both Federal and local laws, so be sure to check regulations before making modifications involving any emissions control device.) If your truck's converters need to be replaced, installing high flow models, such as those offered by Random Technology will pay off with increases of 8-10hp across the entire rpm range. GM's 5.3-liter engines are equipped with a Y-pipe that incorporates a converter for each cylinder bank. Replacement of the converters requires that the originals be cut from the Y-pipe and the replacements welded in their place.
One of the best ways to take full advantage of flow improvements made to an exhaust system is to make similar improvements to the intake system. Replacement of an original equipment air filter element with a low-restriction type is a no-brainer. However, a number of studies have shown that some brands of high performance air filters don't do a particularly good job of filtering. Issues seem to arise only under extremely dusty conditions, but it's a good idea to periodically check the intake ducting between the filter and the engine regardless of the air quality that normally surrounds your truck. Not only will you be able to determine whether the filter is performing satisfactorily, you'll also uncover any damage that is allowing unfiltered air to reach the engine.