Having now had a full inspection 2 service (included spark plugs) on our newly acquired 40k mile '03 4.4 V8, the previous slight mis-fire around 2k rpm on a light / constant throttle or under load whilst climbing a steep incline appears to have disappeared however there still seems to be the mother of all flat spots whereby I can push the accelerator pedal quite a way with no material change in forward progress.

If I knock the box over in to sport mode it changes down a gear and will add as much as 30mph for the same throttle position and in auto mode it will also change down if I push the throttle far enough (but not necessarily so far as the kick-down stop) - is this common to all BMW based 4.4 V8's or might I need to undertake further investigation?

The car is generally quite lively and will pull cleanly from rest right round to the red line, but between 1,900 rpm and 2,300 rpm or so in a high gear and part throttle it's certainly no diesel beater (and therein might be my answer).

Been back to Conrico Service today (the handbrake wasn't adjusted at service) and they put my car on the diagnostic system and it turns out one of the cam position sensors is faulty - that will explain it then!

Looking forward to a replacement on Thursday making all the difference, then it's time for a Prins LPG conversion.