It's really just quality control stuff. The trans slipping is due to the fluid not being to the correct level. Remember the 4Runner is built in Japan, the Tacoma and other Toyotas are built in Mexico and finished in Texas. And we all know most Americans are lazy and stuff gets looked over.
Tacoma final assembly is in both Texas and Baja California, Mexico. There is a myriad of issues that can cause AT fluid fill issues. The transmissions may have come under filled from the supplier. The data about fill may have been NG from the vendor. The final assembly plant usually only adds a certain amount to top off the unit. It could have had nothing to do with the final assembly plant.