D2 running issues - advice wanted

[faffi]

I'm in a situation where the garage says my car is fine, whereas I say it isn't. They have updated the SW twice, and it was actually better after the first update. Issues that I have now are (sorry for being so longwinded) :

- High fuel consumption
- Reduced power in 1st gear - noticeably better acceleration in 2nd gear
- Slow pickup after changing up a gear under acceleration (turbo-lag)*
- Reduced power/sluggish below 1500 rpm*
- Uneven running at low rpm, car often will not crawl along smoothly when sitting in line, sometimes even bucking and lurching to the point where it can only be stopped by de-clutching and starting over again#
- severe repeated cut-out during medium throttle use, went away when floored (worse than a stutter)
- difficult to take off smoothly, car bogs and sometimes revs soar to 2000 rpm without correspondent throttle use - but car still bogs when clutch is released at the approriate speed#
- "misfire" randomly after letting up on the throttle following normal acceleration
- sometimes the throttle pick-up or letting it up is butter smooth, other times it is very abrupt, even though the throttle is used in the same manner#

* was fine after the first update, reappeared after the second update
# appeared after the first update and stayed like this

When I first got the car, I could drive it silky-smooth, like a well-designed automatic or better. The only annoying issues were the high consumption and sometimes a judder when gently reapplying the throttle after coasting.

Now, the car is sometimes smooth, sometimes impossible to launch smoothly. And the judder has gone from something mostly I noticed to something that one fear will cause whiplash one day if a passenger is sufficiently pencil-necked.

Since the car's behaviour isn't consistent, we are down to me either suddenly having forgotten how to drive after 30 years, or the car has some issues. Even if the computer says it's fine. Anybody have some idea of what could be the culprit? What I can suggest to the dealer that has just shrugged it off since the car doesn't have any fault codes to share?