Whistling sound and occasional loss of power

This vehicle could make a noticeable whistling sound under load as it is driven. It does not comes with engine revs as when I rev the vehicle on no load (in neutral) it is not noticed until revs hit excessive 4000-50000 revs.
But when I am driving around and going up a hill or pushing hard on gas it is really noticeable.
Secondly, after five to ten minutes of drive it loses all most all the power. Could not go up an ordinary hill. I do also have noticed black smoke.
The car was parked up for about a year.
I have changed the turbo but made no difference.
Any suggestions will be greatly appreciated.
Thanks