Overheating problems

[scumfromohio]

A couple of weeks ago my car started overheating. It turned out to be a bad engine coolant filler neck and cap. I replaced both those. Then it started starting really crappy like stalling out right after i started it and puttering alot. I figured with it overheating although i was watching and putting coolant in it before i replaced the neck and cap it was probably the ect sensor. So i replaced that. Now it still starts funny occasionally and my heater takes forever to warm up. and the driver side vent gets hot at least 10 minutes before the passenger. And the overheating light will flicker occasionally but coolant is always full and it never feels hot. I checked the oil for a blown head gasket and the oil looks brand new as i just got an oil change. There's no coolant in my car on the floor so i don't think it's a heater core issue. Any help would be greatly appreciated. I don't know what else it could be. It's a 08 yaris hatchback. Only things I've ever replaced was the alternator maybe 6 months ago and the water pump maybe a year ago. It's got 240000 miles on it.