When I first start my truck, it makes a gurgling noise?

It could be the A/C drain that is clogged but it can be also air trapped inside the heater core. Here is a video that shows you how to find and unclog the drain and if that is not the problem start the engine and allow it to get hot, turn the heater on high-speed hot temperature and raise the rear of the car up which should force the air out of the system.

https://youtu.be/q9_MZiS2_NE

and

https://www.2carpros.com/articles/jack-up-and-lift-your-car-safely

Please go over these guides and report back.