Overheating issue

[sjburk]

So my 67 250 6 cylinder keeps heating way up. My gauge doesn't show actual numbers for temp just an h and c opposite each other which is new and also a new temp sensor in the block. Every time I drive or just let it idle, the temp shoots all the way up hot to the right side pretty quickly and then after a moment shoots back down nearly all the way and then never usually gets back above halfway. It also usually will force some water out the overflow hose, no matter how many times I let it do so or add more.The motors been overhauled, It's got a new 3 core radiator as opposed to the original two core, new water pump, new heater core, all new hoses, a brand new 13 psi rad cap, I pressure tested the radiator last week and there were no leaks or pressure loss, and I've replaced the thermostat three times first with 2 195 and lately a 180, but it still heats up that first time and then cools back down like a sticking thermostat. All within the last 6 months I believe except the radiator which is about a year old. I've replaced the thermostat 3 times so I don't think that could be it, it holds pressure, and no leaks are visible so what could be wrong?