All depends on location....if it cold outside this will affect the boost. Cold = more boost + no tune = fuel cut

 

same thing happened to me =T

 

Get the car tuned. The same thing happened to me. If you do not get the car tuned you will start getting a CEL code P0234. All you need is a tune!

 

This isn't exactly like what I experienced but I may be understanding the description wrong or the description could be incomplete. But anyway, when I experienced something like this it was also on an onramp. I floored it and as soon as I hit boost (probably at around the same 5000 rpm) the rpm's jumped up without the car accelerating then it caught and the car shot forward. If you weren't watching the tach the whole time you might not have caught the rpm jump, but it would feel a lot like what you're describing. The cause of this is the clutch starting to slip. I'm only mentioning this because no one else has yet. A lot of people that are much more experienced than me are saying you need a tune and I have no reason to think they're wrong but it's worth checking all possibilities.