Truck running out of coolant

I think you may have a blown head gasket. Look online, there is a way to test it by simply cranking the motor.

You need to pressure test the cooling system. The coolant may be leaking inside the engine or possibly a heater core. A pressure test should show where it's leaking.

When you pressure test the cooling system it should hold the pressure for 15 minutes minimum. If not, you have a leak. You can check for a blown head gasket by starting the engine with the cooling system under pressure. If the needle on the pressure tester gauge bounces, you have a blown head gasket. Another possibility is a worn timing chain causing the engine to heat soak after you shut it off. When that happens the coolant can boil out of the plastic recovery tank! Lastly you may have a leaking intake manifold gasket if it's a V8 engine. Hope that helps! Jim

Another thing I forgot to put is that under the hood there is a coolant smell constantly

Check the intake manifold gaskets. My Caprice was leaking coolant from the intake manifold for a few months before I finally found it! It was a very small leak but I kept losing coolant and could smell it under the hood too! Hope that helps! Jim