A 10W-30 oil is going to be at the same viscosity than a 5W-30 oil at high temperatures, but it will be thicker at lower temperatures.
Since you are in California (high temps), you should use an oil that has 40 or 50 as second grade.
On my side, I use Shell Rotella T6 (5W-40) It is a tough synthetic oil that is formulated for diesel engines. It has good characteristics and is easy to find and cheap.
I think that Toyota recommends 5W-40 in the 3S-GTE, but I am not sure.