Nope, once I made a mis-judgement getting on the highway in my 951 about 1 minute after starting it, it ran right up to 6000RPM no problem at all, and it was mighty chilly that morning.
AFAIK, that is BS.
Sounds to me like loose speed/reference sensor connectors, that or they're broken or corroded or something.
When I broke one of the connectors for my engine speed sensor, once I got around 4500RPM it would get very very jerky, since it vibrated just enough at that speed so that the connector didn't make contact. Eventually it started doing it while I was just driving around, or when I hit bumps, and I replaced it.