NHTSA Complaint #11688929 — 2021 AUDI Q5

My car always did a weird shuddering thing when taking turns a certain way. I just thought it was part of how the new vehicle worked. I thought it was strange when I took my car in to repair a front tire, and was told / showed that the back two tire treads were worn down. The new car only had 20,249 miles. But I read somewhere that some new car dealers use lower tread tires to save money, so I did not pursue anything. Then, when someone pointed out that the 'weird shuddering' was not normal, I took it into Audi to have them look at it. Audi did a repair, and said I had to drive it 600 miles to know if it would be resolved. After the 600 miles, the problem continued. I took back, and they said they know what it is but they have to go through certain steps first. They told me this time that the good news was that they would replace with a new center differential, but the bad news was they were not sure how long it would take to get one in. I waited patiently, and then received a call saying it was fixed, (but they did not replace the part). What I did not know at the time was that a message was left 10 minutes earlier saying the part came in and they would be replacing it. After further questioning, the Audi guy said the new 'fix' heats up the fluid better and allows it to work its way through better. He said he was informed moments after he left the VM (where he said they were going to replace it), that the technician told him, and he took it for a drive, and it was 'fixed.' He then told me what he drives, saying his does it too. He said the technical bulletin says i must drive 250 miles (again) and later when I picked it up he said 500 miles. I pointed out my concerns regarding the safety of driving a malfunctioning differential (loss of traction, poor handling, and the potential for complete failure while driving), as well as uneven tire wear. He emphasized that it's fixed and completely safe, even though they did not replace like I was told they would.