The answer to your question is yes, Ford still recommends 5W-30 for the new SOHC engines. But that doesn't mean shouldn't use a 10W-30 in your '99 during the hotter summer months, and in fact, that's probably what I would do if I lived where you do.
I have a 2005 Explorer with the 4.0L SOHC V6. I just changed the oil and used Mobil 1 10W30. Have the engine tolerances tightened since 2001 and should I be concerned?
No. The change to 5w oil in all engines was driven by the need optimize fuel economy. Everything that can be reasonably changed to improve fuel economy is being done, driven by regulation and market demands. Some items such as electric power steering ilo engine driven hydraulic make a noticeable difference, some such as going from 10w to 5w oil is a minor change. Expect to see 0w recommendations.
You are good to go for as many miles as you wish to keep the vehicle.
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