2002 Other Chevrolet Models Overheating

Engine Cooling problem
2002 Other Chevrolet Models Four Wheel Drive Automatic 61,000 miles

My 2002 Chev Tracker was having problems with heater not blowing hot air unless we were moving. So I replaced the thermostat. Checked heater core as well. Well husband was helping so we lost some antifreeze I was perpared for it and had something to catch it. The next day we went for a drive and got about 2 miles and cool air started to blow again and engine heat started to creep into red. Shut it off. We checked the oil for a weird color (to see if antifreeze was making way to oil) as in gasket blown no odd color.

We kept going as long as hot air was blowing the car temp was perferct but seconds after cool air would come out temp would sky rocket. I checked the floor near the passengar side and such for wetness (I know it will get wet if heater core is dead. Dry as a bone. Thinking something with radiator but could it be something as small as vapor lock? I lived with 3 mechanics when I was growing up so I know a little. But if I try to fix the vaor lock by taking off the cap and letting it run, I could do damage if the temperature goes high. Any suggestions would be appreciated.