You know, I thought that was normal. My engine does not like to be revved when not at normal temp. It always hesitates a bit at low RPM when cold and it is my understanding that cold engines suffer a lot from revving so I always keep it under 2000 rpms until fully warmed up. This is why the new M cars have that dynamic redline that goes up as the car warms up. When I had to change my transfer pump I was suffering from high rpm fuel starvation.