FS2004 Rotating Speed

Does anyone know why FS2004 planes (Boeing 777 & 747) start to rotate at
98kts when taxiing down the runway, whether I use the TOGO switch or manually
by F3 key? Flaps set to 5 or 10 depending on plane being piloted. Once
plane has gotten airborne, it goes into a steep climb and stalls. If I press
the CMD swith, it goes into a higher climb even though I have set my VSI to
700fpm.

Thanks