Clutch slip

[Bigsi15]

Morning guys
Regrettably I find myself on here AGAIN with an issue. I'm finding I'm getting what I believe to be clutch slip especially in fifth gear under full throttle. This seems to have come about since sticking a superchips stage one tune on the car pinched from my brother. The clutch is new and has done about 10,000 miles of gentle driving and is a genuine 850r clutch from Volvo including pressure plate and release bearing. Flywheel was skimmed. Seemed to be fine on the stock tune and I seem to think it being okay initially on the stage one but now I'm getting nearly 500 rpm surges that are not correlated to speed under full throttle at about 70 mph which then drops back to where it should be. Initially I thought it may have been wheel spin related but pretty sure it's not now as surging is getting worse.

I've got no sign of the rear main seal leaking or any oil contamination down there and the rms oil seal is new as the engine was rebuilt

I've included a photo of the map graphs to show what it's apparently putting out as tuning is kind of new to me but I thought the 850 r clutch should be easily able to handle 250 hp or more. My brothers car seemed fine with it and if anything is less supporting modded than mine is

Can anyone think of anything else it could be?

Thanks