I live in Phoenix which gets hotter than Houston and stays hot longer. I have never ran anything but the Ford recommended 5W30 in my '97 SOHC. I have put 92K troublefree miles on my Explorer without ever using a drop between the 3K-5K intervals that I follow. Ford is now starting to recommend 5W20 over the last couple of years. I would stick with what Ford recommends. I'm sure they spent a lot more resources and Engineering time to determine what is right for your Ford engine than your local mechanid has. It won't hurt anything either way though but I doubt if you will see a benefit either.