Car has started to not take off from rest, unless you rev it up

Take off normally, car slowly builds speed until turbo kicks in. 1.9 DCi diesel. Turbo replaced last July. Twice since then, have had to put 2-3 litres of oil in to top up between changes. Oil present in turbo pipe, before turbo. In the last few weeks, if I take off with increased revs. No problem and turbo kicks in just under 2000 revs. No smoke. If I take off as normal, car builds speed slowly, until turbo kicks in, she then accelerates away with a large cloud of grey / black smoke.

No problems at cruising speeds, but if I accelerate hard, with revs below turbo kick in, car takes time to build speed, turbo kicks in and car accelerates with smoke trail until what I presume is all the unburt diesel is gone, then clear exhaust. Has got worse since originally noticed.