Hello, I'm Danny.
This video shows the job being done on a similar car but the process is the same. Here is a guide to help you step by step with instructions in the diagrams below to show you how on your car.
Yes, I would recommend changing the thermostat since you will be draining the coolant out.Both the water pump and thermostat when purchased will include new gaskets.As far as the RTV (gasket sealer) goes I recommend Permatex brand ultra copper. Here are a few tutorials showing how to replace a water pump and thermostat:
I've attached picture steps below on how to change the thermostat and water pump below for your F150. Check out the diagrams (Below). Let us know what happens and please upload pictures or videos of the problem.
Images (Click to enlarge)
Friday, May 15th, 2020 AT 4:40 PM