Misfire?

["Ian J Haseltine" <Jim_Haseltine@msn.com>]

Anyone BTDT - under firm acceleration, ok to 4000 rpm, then slight power loss, 
maybe missing, just enough to notice although engine still pulling, back off 
slightly and engine continues through to above 5000 smoothly.
Hard acceleration similar except much more obvious and engine sounds  rough 
but still pulls.

What am I looking at here - misfire, overboost, fuel probs? Any suggestions 
will be welcomed. I'm going to have it run on a rolling road soon but I'd like 
a few ideas before I get my cheque book out.

Thanks

Jim Haseltine
88 Ur quattro