I was Driving On The Highway One Nite And I Was In 3rd at About 3200 Rpm and Instead Of It Moving Forward The Rpm Dropped and The Caught Up....

I knom car when its slippin it usually goes forward in Rpm's and kinda over-rev's...

What Is The Cause Of this and how can i fix it...
2002 audi tt 180hp
front wheel drive
5 speed manul