2 problems - cold start & revving

I have 2 problems currently on my R-Reg 1.8 TS 156 ~145,000miles;

Cam Belt and Variator were done 2 months ago (also upper wishbones and
anti-roll bar but that's not im****tant)

First of all I seem to be suffering the old Cold Start problem
re****ted here several times (but no satisfactory answer given
searching back...) upon cold starting revs rise then drop very low.
upon opening throttle the engine splutters and coughs. If the engine
is revved above about 3000 revs it sounds ok but below this is crap
and can barely pull the car forward. This clears after about 30 odd
seconds or 1/4 mile of driving. 
I've had a quick look at the throttle butterfly valve with my
mechanic, he'd fixed up a similar problem on a 145 (i think) by
cleaning a sensor there. We used carb cleaner to dissolve off all the
black gunk in there (also checked the various plugs and whatnot)
The problem is slighly better and she certainly revs more freely now
but it ain't fixed. any ideas?

Secondly the engine has problems revving over 5000 revs, it was crap
before I had the belt and variator and has improved muchly but it's
still not right. It feels like it's running out of ooomph and an
upchange of gear gives much more pull straight away. Having driven
several Alfa's recently; (a couple od 155 loaners from the garage and
the 156 Selespeed i've mentioned here before) All of which had no
problem in revving right up over 6000, i'm concerned there's some
thing horribly wrong here.
I've checked the plugs and they are all fine, they look new as well so
I expect these are the cars second set.
Air filter is new (ish) however I haven't found the fuel filter/ pump
yet and oil needs a change.
Any thoughts?

Additional: I'm going to the Cloverleaf club track day at Brands on
the 4th June; anyone been on one of these days before?

Thanks in advance,

Ted