My wife drives our 04 s-line with 110,000 miles. I drove it last week for the first time in a month. The first thing that I noticed was when accelerating quickly the engine wants to rev up quickly to 5,000+ and stay, like the transmission is slipping. There is a noticible loss of power and can only accelerate without the over rev is by slowly applying gas. Other wise the engine runs very well. All maintance is regular and current.

I had the transmission replaced with a new one 10,000 miles ago, the original trans lost 4th a 5th gear in a big way! (Bang)

Is this a problem with the transmisson / turbo / o2 or something else?

 

Well, if you had a MT6 I would suspect a slipping clutch. When mine went, under heavy throttle it would rev to red line (and beyond if I did not back off) while the car barely accelerated. So, what is the equivalent in a tip? The torque converter? Was it a new or a rebuilt transmission and do you have a warranty?

 

All new Trany and TC. I really dont think that it is the trany, it shifts storng and smooth.

As I did not list in OP its is a A6 2.7.