As Paul pointed out, a factory tow package includes many upgrades. Whenever a vehicle is used for towing, the extra trailer weight can easily equal the weight of the towing vehicle. This adds extra stress and wear and tear. The tow packages specifically address these issues, in an effort to increase the reliability and safe passage of the vehicle.

When towing, the main concerns are additional heat to the drive train, the carrying capabilities of the frame, tires  and suspension, and upgrades to the braking effort.

On a used vehicle, the drive train reliability can be quickly addressed, by replacing all the lubricating fluids with synthetic products. This will lower the operating temperatures and reduce any further mechanical wear. The specific items would include the motor, transmission, transfer case, and both axles on a 4X4.

The cooling system should be professionally flushed and new antifreeze installed. The thermostat should be replaced. When the truck is used for towing, and if the engine temperatures are found to be too high, a larger or modified radiator should be added. This will also lower the transmission temperatures.

The brakes pads should all be replaced with top of the line products, and upgraded front rotors should also be contemplated.

The trailer's brakes will be very important, and must function properly. They should be inspected, replaced if necessary, and properly adjusted. The truck's brakes should not be the only braking effort for the rig. A brake controller should be installed in the cab; some manufacturers have the necessary wiring already installed under the dash and run to the rear bumper area. A new multiple pin trailer plug will have to be installed, to facilitate the use of the brakes.

Tire upgrades may be necessary. Many light weight trucks have tires meant for ride comfort instead of load capacity. Especially on the rear, a higher capacity LT tire, will enhance the load capacity and reliability of the truck. The shocks should be replaced on or before 40K miles, especially the rear. Purchase the best name brand HD shocks with a lifetime warranty. Worn rear shocks can greatly negatively affect the towing capabilities and safety of the rig.

Many people safetly and reliably tow with half ton vehicles. You shouldn't exceed the manufacturer's towing specifications. Except for changing axles or ratios which can be somewhat addressed with an automatic transmission, most trucks can be easily upgraded for towing. If you are purchasing a new vehicle, the tow packages are a bargan, and well worth the additional funds.

Great information, thank you!!

I am looking at "normal" Silverados with the 5.3 engine. My current vehicle is a 95 K1500 with a 5.7 engine and HD towing pkg. I have no complaints about it; I bought it new and it towed fine for all these years. But it's time for a different vehicle. I am having problems even telling if these used Chevys have the Z82 pkg on them...is there any way to tell if they do?