You can engage TACC only with one downward push on the gear selection stalk. That does not engage Auto Pilot, which requires two pushes.Can you turn off lane centering and just use the TAAC? When I'm in traffic cruising 5MPH I don't really need lane centering, just TAAC. Are these mutually exclusive capabilities, or required to work at same time together?
I recommend reading the Model 3 owners manual starting on page 61 where TACC operation is explained. See https://www.tesla.com/content/dam/tesla/Ownership/Own/Model 3 Owners Manual.pdf