Those comments on…
Those comments on aftermarket modifications affecting performance including mileage is true in most instances. I have been in the automotive industry for almost 50 years and have dealt with those concerns. Unfortunately I’m not sure if that’s what he is dealing with. I also purchased a 2021 Tacoma TRD and from day 1 and 6 miles on my truck it did the same identical thing. Mileage is about 15 mpg and downshifts all the time, especially with the cruise on.
No modifications have been made! Factory tires, wheels, no special tuning and no lift kit. NOTHING!! I spoke with the dealership and was told that it was normal. Why he was not experiencing anything until now is anyone’s guess. After years as a tech, parts manager and service manager the problem feels like a programming issue to me.