clutch slip or overboost?

Took the car for a pretty hard drive today across some serious whindy and very steep mountain roads.

The pull through the gears was great coming off hairpins, braking hard, pulling through the gears again. All no problem at all. Great fun!

But as soon as I got back onto a dual carriage way and had the chance to peg it flat out coming off a roundabout it seemed to flat spot slightly in third at 3000 revs then come back in then flat spotted again in 4th at 3000 revs and come back in again.

But on the steep hills where you would expect clutch slip there's no slip what so ever.

Is this overboost or the clutch??

Remapped to 165ish.

Ps. No crazy speeds were achieved, just pushed it hard until I hit 70ish then just cruise along.

Nothing wrong with getting to that speed as quick as you can.

Also revs dropped slightly and not shot up!

Techies, help!!