A radiator is supposed to get cooler from the top down, because the hot water enters the top of the radiator and then as it makes its way down to the bottom, the air flow cools the water or coolant.
really need to a few things:
1. do the cooling fans work properly? turn on the A/C , they should come right on.
2. is the coolant circulating through the radiator or is it plugged up?
3. Does the water pump push the coolant through the engine fast enough?
4. Is the new thermostat working properly, can you feel it open when the engine gets hot, you can easily test this by letting the engine warm up and the bottom hose will be cool at first, then as the thermostat opens, the bottom hose will get hotter and hotter, this MUST happen.