MB 300SD bogs down when I decelerate after leaving highway and accelerate at the end of the ramp. Noted in diesel mode only. Runs fine otherwise. Runs 80 mph and then feels like is has air for 10 seconds and then goes back to normal.  Seems like maybe sucking air.  Filter change did not fix. Full tank so not gulping fuel. I was thinking may be a small air leak that high vacuum from decelleration causing a bubble, but it would have to be pretty close to the IP as it happens as soon as I try to accelerate.  Ideas?