It seems Toyota Tundra engineers went a little bonkers with respect to self-programming of factory keyless entry remotes a decade ago. Toyota used keyfobs with FCC ID GQ43VT20T on many vehicles from as early as 2004 to as late as 2017. This family of remote transmitters was used on Avalon and Solara sedans, Sienna vans, Highlander and Sequoia SUVs and Tacoma and Tundra trucks. In short, they appear on a lot of vehicles. See the many GQ43VT20T remote button configurations at the following link: Toyota Remotes with FCC ID GQ43VT20T
For many vehicle model years, these parts are user-programmable, meaning that an owner can program the vehicle him or herself to add a new remote transmitter. Up until the 2008 model year, every vehicle that used this part was user programmable. Then, for some unknown reason, Toyota changed something so that 2008 Tundras require a special computer “scan” tool for programming. The following year, Toyota switched back so that 2009 Tundra trucks were again user programmable. And then, in 2010, they switched back for good to requiring scan tool programming. This kind of flip-flopping is very unusual in the auto industry, though not unprecedented.
Maybe Toyota engineers just want to keep us all on our toes?!