Not sure what's going on there Phil.
I have never experienced that problem in mine.
In regards to driving it first thing in the morning when its cold, mine is very spluttery if it goes over 3k rpm. But as soon as its mildly warm its fine for the rest of the run (whether its a 5min or 5hr drive).
Hope you can find the problem, fix it and let us know for future reference!!
- Dave.