The easiest way to be sure is to go out to the truck and measure them.
If you go into an auto parts store, they'll ask you if you have 16 or 17 inch wheels. If you say 16 they'll sell you the 12.5 inch rotors and if you say 17 they'll sell you the 13.3 inch rotors.
In reality, it's not that simple. I have an SR5 with 17 inch wheels but it uses the 12.5 inch rotors.
I'm sure that people will chime in and tell you that all SR5s us the small ones but the Limited and Sports use the larger ones. That may be right, I don't claim to know. The best way to make sure is to just pop off the wheel and take a tape measure to your current rotors.