As we were out and about in it yesterday (needed the boot space), we were joking about it's (lack of) performance, and as we got onto the motorway, we wondered if it would get to 70 by the end of the slip road, neither of us thought it would. But it did

So I kept my foot hard down (yes, I know Mr DTM, but gives more consistent results) for several miles just to see if a good thrashing would help clear its throat.
Speed was more than I'd seen out of it before, esp after a long downhill section, but after a while, and more prominent on uphill sections, you could feel the power surging in and out, very rhythmically, about once every second or 2. I'd say this was the same sensation or the surging that MDTM felt driving around at low revs, that was initially cured with a replacement, pattern MAF (that low speed surging has returned slightly, nowhere near as bad, when labouring around 1500rpm). As per the low rev labouring surging, lifting throttle slightly, and it went.
Does that shed any more ideas?