Changing coolant

The 3 gallon capacity is when the engine and cooling system are dry as when it was first assembled. When you drain your system about half come out becasue of the below drain areas of the block and heater core etc.

The best thing is to do several dump and fills with water and on the last dump add pure coolant and top off, this will give you a 50/50 mix.

Here is a guide to help you get the job done.

https://www.2carpros.com/articles/coolant-flush-and-refill-all-cars

Refill the motor with water and run it, drain it several times until is pretty mush just water in there. You'll need to let it circulate each time until the temp gets high enough to open the t-stat and access the rest of the system.

If your adventerous, you can remove the t-stat when you do this to get complete circulation witheout getting to temp.

A savvy owner of a truck like yours will keep a very close watch over the next 60,000 miles as a intake manifold gasket leak WILL happen. Various symptoms such as overheating, oil or coolant loss, misfire codes or a yellow slimy appearance on the oil filler cap begins appearing; will indicate the need.

https://www.2carpros.com/articles/engine-overheating-or-running-hot

Please let us know if you need anything else to get the problem fixed.

Cheers, Ken