Thermostat or a water pump?

Hi so I'm going to try and make this as clear and straight forward as possible. So my car started overheating and I didn't know why eventually it led to my radiator cracking. I just replaced the radiator yesterday and I test drove it to see if it's still overheating. It was fine driving around the neighborhood but that changed when I took it to the road. It went hot. I'm glad there weren't any old people to get in my way before it blew. I filled it with fresh coolant but when I got home I checked it and my reservoir was empty. My car doesn't have a radiator cap. I did notice before that when I would drive it would start to overheat but would settle down while I drove but would go back up when I stop at a red light or something. When I test drove it, it just went into the HOT but didn't go down while I was driving. It did the other day before I replaced the radiator. I drive a 2001 Ford Escape XLT V6 3.0L 2WD. So could this be a bad water pump or a bad thermostat? I would like to know before I just start buying stuff. There's a difference between the prices. I know you can't do as much without seeing it but my car can't go anywhere because of the overheating. What do you think?

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