Or drop in pressure

On sticking my foot down at a reasonable rate when in 4th gear the revs go up and as they past 4000 Rpm and it hits 4500 the needle then drops back to 4000rpm then carry's on upwards as normal???

This is my first turbo car so bit concerned.

Doesn't seem to do this all the time?

Any advice would be much appreciated

 

does the engine race and drop? may be a bit of clutch slip by the sound of it?

 

In 4th gear as you accelerate and hit the 4500 mark it drops back to 4000 then proceeds upwards but seems hesitant on increasing the Rpm from 4500 upwards if that makes sense.