Puma 2.4 stuttering & weird speedo issue

Hi all,
I had a turbo underboost issue on my 2.4 and the turbo vanes had seized.
I replaced the turbo which didn't cure the underboost (but needed doing anyway) but I started noticing a stuttering of the power when accelerating. Weirdly when the stuttering happens, the speedo also went haywire or stopped completely until I took my foot off the gas, then it was ok.
So today I replaced the intercooler - no more underboost (YAY) but the stuttering and speedo issue is still there.
It seems to only occur after the engine has been started hot.
What could this be? Could it be an ECU issue? I wouldn't be surprised if the car has been remapped in the past - could this affect it?

Some have suggested elsewhere that this could be due to the wiring on top of the turbo not being seated correctly.
Will have a look, if it stops raining!