Should I 5w-20 or 5w-30 synthetic oil in my sequoia 2008 4WD where temp. are 100 - 104 degrees F?

"The manual suggests 5w-20 but I am advised to use 5w-30 due to thehigh tem in the rea I am using the truck."

In that kind of heat 5W-30 wouldn't be a a bad idea. Though 5W-20 would likely be fine.

"I checked at most of the lub stations and they do not carry both 5w30 and 5w20. They carry 15w40 and 10w30"

You're not in the U.S. I take it. In the states, literally every oil change place or mechanic in the U.S. and Canada. will have an ample supply of 5W-20 as it's been the most common oil for the past 15 years or so. In developing countries where old cars are more common and there aren't many laws regarding emissions, heavier weight oils are still common. You need to be careful with modern cars in these areas as often the oil the locals have for sale will not meet the same specs as oils found in first world countries. Pay close attention to the API certification. You should be using oil with an SN or at worst, SM, rating, anything less than that shouldn't be used in your vehicle.

stay with the recommended 5w30. If I had to, I would move to 10w30, being a little thicker rather than the thinner 5.

Your engine runs at around 200 degrees. It really doesn't care if the outdoor temp is 100. Use what the car maker recommends. Period.

Just use Mobil 1 5w-30 wally world carries it. Take the correct amount with you to the shop and tell them to use that oil for the change if you cannot change your own oil.

? Any lube station that doesn't carry 5w20 or 5w30 doesn't deserve anyone's business. These are standard weights.