Check your owners manual to see if you have a button to disable “overdrive”, it’s for adverse conditions such as uphill or downhill, off-road or rainy, etc. It prevents the shifting up too early and gives each gear more range to operate in. By default it’s on because it saves fuel, and they make the button hard to find sometimes.
Even if they did go through the trouble to do their own taxes, the IRS specifically instructs taxpayers to not calculate it themselves, but rather to use a “tax table” to lookup their income and next to it is listed their income tax amount.