Is my tranny going?

I brought my car in to the dealership for a fluid change and I've noticed a big problem with it since I've gotten it back. At 80-100kph and hovering at 2000rpm it does not accelerate even when the pedal is depressed. At the same time, I can hear the engine free revving (kinda like being in neutral), but the tach still shows it at around 2000rpm and not moving. I also dont percieve any acceleration or deceleration.

It doesn't happen all the time but only when I've been cruising for a short while at the same pace. Is this the first sign of my tranny going? 140,000km.