2000 ford ranger coolant system problems?

I have a 2000 ford ranger and was having problems with the coolant system. I flushed my radiator and put new coolant into it because i was told my radiator might have been clogged so flush it. After doing so it was still pulling coolant over and bubbling in the overflow tank. My heat would not work when i first turned on my vehicle and cause the coolant to burst out of the overflow tank. My temp gauge was in the middle at normal temp the whole time. I changed the radiator and cap, put new coolant and burped the system getting the bubbles out and replaced the thermostat and heater valve. I drove the vehicle for about an hour and when i checked the coolant in the radiator when it cooled down it had again pulled coolant out of the new radiator and put it in the overflow tank. Any ideas on what it could be would be greatly appreciated.

Only thing I question with your work is the radiator cap. The caps are specific to each model or vehicle. If yours calls for 15 lb and you put a 12 lb cap on there, it will release early into the reservoir. Check the number stamped on the cap and compare to the old one. And vice-versa if the new cap is higher lbs than stock it will never release and cause hoses to burst.

Blown head gasket.