The most important thing to do is to get that crappy old coolant out of your engine as soon as you possibly can. It may only have 50K on it, but it is at least 7 years old...
If you want to use just plain distilled water to flush it until that flush water comes out clean, do so.
I strongly suggest replacing it with a CAT EC-1 rated ELC coolant.
If you have an International Truck Dealership nearby, you can use their Fleetrite ELC.
If you don't have an International dealer close, you can use this coolant
available at O'reillys autoparts.
You can use any ELC coolant that meets the CAT EC-1 rating.
Absolutely get a coolant filtration on there also.