I have a 3.0 V6 manual S-type year 2000

If I am driving at say 1500 revs and "boot" the accelarate pedal, firstly the revs rise
and then the car seems to catch up (revs drop a bit)

is this clutch slippage?

Do i need to

a) drop a gear as changing the clutch won't make any difference
b) clutch slipping problem - change the clutch
c) it's something to do with the traction control/ecu etc and don't worry about it.

In normal accelation thro the gears, no problem.
If I drop a couple of gears again no problem
Have plently of clutch pedal