the book says that warm weather calls for 0w-20 (i live in florida).
I'm pretty sure it doesn't say that.
I would go with 0w20 as stated with oem. Mainly due to the vvti system which is sensitive about different weights.
They're not different weights.
They are multigrade oils. The viscosity changes with the temp.
Both oils are rated as a 20 weight oil at operating temp.
At start up temps, 5w will pump down to -30*C.
0w will pump down to -35*C.
It will never be -30*C in Florida.
The "w" after the first number does not stand for "weight". It's the cold weather rating of the oil and related to the first number.
The more important number is the oil's operating temp viscosity.
Both are 20.
Unless he plans on doing an Antarctic expedition with his truck, he doesn't have to be concerned with the 0 or 5. As long as it's a 20.
Also, you guys obviously have a computer and internet access. There's no reason to not know this stuff in this day/age. There's no reason to make assumptions or base decisions on myths and forum opinions. All the info is a button click and 15 min of reading away.