My 1997 subaru impreza outback is overheating over 335,000 miles.

What is your question?

My car overheats alot I thought my thermostat was bad so I took it out. It was bad it wouldn't open in a wood stove more or less. Someone told me during the summer you dont really need one so I never put one back in it yet. It was doing good for about 2 weeks then started overheating the same as it did before on the highway it only starts to over heat when you drop under 60 mph but when I drive it even if it doesnt get really hot I have to at a little water everytime. It has gotten death hot once or twice when I was in the city surrounded by traffic where I couldn't really help it. The water pump was changed by my father when he had it about 2 years ago. I put stop leak in the radiator not sure what brand but it was orange didnt help none. I'm no real stranger to working on vehicles of any sort but I am far from professional. Any help would be greatly appreciated thank you in advance.

What makes this problem better or worse?

She doesnt like going slow so I adapted a lead foot to accommodate.

How long has your 1997 Subaru Impreza had this problem?

About a year and a half