My 2006 Powerstroke with about 140000K miles on it has started blowing black smoke out usually on acceleration. It has no power when it does this and then if you shift down or take your foot out of it for a second the black smoke stops and it goes. It is also making a slight whistle sound occasionally. I am pulling a 4 horse trailer with this thing and need to figure it out as soon as possible. Thank you for any advice or help.