Odd Gearchange

[The Monzta]

Over the last few days I've noticed my transmission doing something odd only when under hard acceleration.

As it accelerates the revs rise normally and all seems fine but as it changes up to the next gear it momentarily hesitates, the engine note flattens out and the car ever so slightly decelerates then it goes into the next gear and carries on accelerating as normal. This odd fluctuation takes just a split second but it feels and sounds horrible.

I've looked through some other transmission threads on this forum for something similar but there's just too many to look at. So if anyone has any idea what is happening it'd be very much appreciated.