Hi I have a twin turbo mini coupe and lately it is losing power when I accelerate hard. Usually when my revs are around 4000-5000 RPM. It use to rev to around 7500. I have to back off slightly or change gear. So if I take off in 1st, once it gets to around 4000-5000 RPM it kind of puts the brakes on so I change to 2nd and accelerate hard again but the same thing happens when I reach the same revs, so into third but the revs never seem to get up that high so I keep accelerating & changing up the gears. Any ideas? I've told mini garage about this problem but I think they don't want to know about it.