Most people who buy trucks probably do it because they have stuff to carry around, and that's fine. A truck can certainly carry around more than a car. But, even though we've already discussed that even trucks have their limitations, it's important to realize that those limitations are, in fact, important.
We've already explained how tow capacity ratings work, and why it's important to stay within them. The same principle applies here. So, why did we bring it up again? Well, it's to prove the point that, just because your truck has a hitch doesn't mean you have additional capacity to tow. A towing setup does not in and of itself increase the weight burden your truck can safely carry. You might have the extra equipment that physically enables the towing, but your engine will still feel the extra strain if you're carrying more than you should.
You have to consider a truck's total burden when determining its capacity. You can't load up a trailer to the tow limit, pat yourself on the back while congratulating yourself for your own cleverness, and then totally disregard the weight of a bunch more stuff that you've dumped in the bed, strapped to the roof, or stuffed in the cab. It all counts, no matter where on the truck the weight is being carried.
This is especially important if your truck wasn't originally equipped for towing -- that is, if your tow kit was installed after it was sold, by you or a mechanic. That means your car's manufacturer wasn't considering towing when it published your model's tow capacity rating. Some experts suggest that if you have an aftermarket towing setup and frequently pull heavy loads, it might be possible (and a good idea) to upgrade the radiator, water pump and coolant lines to help dissipate extra heat [source: Pro Car Care]. You still shouldn't push your truck beyond its limits, but your engine will be better equipped to handle the extra work.