1996 Cadillac El Dorado I really need help finding my overh

I really need some help, ive checked my thermostat and is working since it opened and closed when i checked it, i also checked the water pump to see if it was leaking and didnt see any leaks, I was told that if it would be my radiator it would stay overheating for a good period of time but it cools down when i stop driving so i figured my radiator seems to work. The problem is that i drive for atleast 15 to 20 minutes for a good distance then it starts over hearheating. I stop for a while and cools down pretty fast. So far ive put a new thermostat new water pump and upper and lower hoses. I also found out that my car had been sitting for more than half a year before i bought it so makes me wonder if the radiator is clogged up but if it was should the car over heat for a longer period of time?? I had a guy check it with a tester and gave me codes that i had to get at autozone which where p1258, p1153, po306

p1258 = 1. low oil/pressure 2.blocked oil passage 3.failed vct oil control valve.

p1153 = 1. Failed H02s-21- heater circuit 2. h02s-21 signal shorter the ech ground 3.improper oxygen supply to sensor - check sensor connector and wires.

p0306= Ignition system fault-spark plug(s} 2. vacuum leak 3. Injector fault 4. high or low fault pressure.

Thats where im at right now. Can someone please help me i dont have anyone who can help me and im really strugglin. Anyone with any type of info. or ideas please let me know. Thank you!