Hi and Help

Hello to you all, I have recently returned to RR ownership with A 96 p38 TD. I have had all the usual problems and managed to sort them....electrics etc. But and here it is , I have lost power above 3000. I hear the turbo whistle but there is no power there. In neutral it revs fine, and has just brought me home from work (70 miles) without a hitch. Any advice would be greatly appreciated. I have checked the intercooler hoses and they are not split....please help. Thanks.

Just an update for future reference - split air filter ! Car now back to normal.