S60 D5 lacking power

[steviemac3]

Im new to this forum and wondering if i could be pointed in the right direction, thanks. My girlfriend has a 2002 S60 D5 saloon with 140,000 mls on with full service history. When she bought car around one year ago i found it lacking power as i read they were nippy engines. I foung the intercooler to be holed ,and replaced. When i took it for a run afterwards it took a few miles still lacking power, then all of a sudden there was a spluttering and a huge plum of black soot came out of the exhaust and the car took of like a torpedo, so im assuming something has been choked and after this has cleared itself.
It ran fine for around 6 months and then when she was on holiday in Glencoe during winter, in the snow the car had a flat battery one morning and she had to get a jump start on a hill.
Since then it has been lacking power the way it did when the intercooler was holed. It revs all the way up but does slowly and slower than it should. It is as if the turbo it not cutting in, although you can hear a slight whistle when driving.
In last couple of months , i have changed fuel filter and air filter. At weekend i checked all vaccum pipes for breaks or holes and found there to be suction in the pipes at the sensor next to the air filter they go to. I also removed and cleaned the turbo vaccum valve above the starter, i then stripped off and dismantled and cleaned the complete EGR valve assembly (which was very sooty inside). I also checked the intercooler pipes for leaks and found them to be ok. When you rev the car, THE BOTH intercooler pipes swell up (is this normal). The car has been on a diagnostic machine which said no 5 injector weak. So i replaced this with a reconditioned unit and all this has made NO difference.
PLEASE HELP SOMEONE lol before i lose my sanity. The car computer is reading average fuel consumption 40mpg still. I also found the both intercooler rubber hoses had a bit of oil in them