See if the lower hose is collapsing when the engine is sped up to highway speed rpms. If it is, you found the problem. I saw a video on Youtube about overheating problems, where sometimes people forget to transfer the 'spring' inside the lower radiator hose when replacing the lower radiatior hose. Is it possible that is the problem?
Also, have you added enough coolant to the system and burped it to ensure there are no air bubbles in the system?
Also, when you replaced the coolant in the system, it should not be pure full strength coolant but diluted down with distilled water to a 70/30 ratio of coolant to water, or ideally 50/50 ratio of coolant to water. Too much antifreeze will not cool efficiently. Water is required to activate the chemicals to cool properly.