You did mix the anti-freeze with water, 50/50 ratio, correct? Pure anti-freeze does NOT cool very well, it needs to be mixed with water.
BTW, pure anti-freeze has a higher freeze point as well, its freeze point actually lowers when you mix it with some water.
Did you replace the thermostat? I do every couple of years and any time I do major maintenance on the cooling system. They often go bad, one way they can go bad is that they will stop opening or closing fully. When that happens, the cooling system will seem normal unless the cooling requirement gets too high or it gets too cold out, either NOT enough coolant flows because it won't open fully or TOO MUCH coolant flows because it won't close fully.
BTW, always use DISTILLED or DE-IONIZED WATER to mix with the anti-freeze, tap water has to many minerals and impurities in it, that will form deposits in the cooling system and break down the anti-corrosion additives in the anti-freeze sooner.
