Q: I smell antifreeze.

If you smell antifreeze inside of your truck then it may indeed be the heater core. Most of the time the passenger side floor will also get wet from antifreeze if there is a leak in the core. A leak under the hood can also cause the smell to enter the cab so you should start with a cooling system pressure test to see if you can locate the leak. A pressure tester is a speciality tool that allows a mechanic to pump up the system to help identify any leaks. For something like this you should enlist the help of a certified mechanic, like one from YourMechanic, that can easily perform this task.