deonwolf

I have recently installed the 737-8/900NGX addon for FSX after having run it successfully on FS2004 for several years.On doing my first proper flight (with cruise altitude at FL350) I noted that while the autopilot (engaged in LNAV) mode initially was able to hold heading it started oscillating (hunting) the required heading with greater and greater amplitudes, to such a degree that aural "bank angle" warnings started going off with the autopilot in some instances turning me as much as 90 degrees off course from the commanded track. Switching from LNAV to Heading Select made no difference either. I attempted to manually control the heading using the joystick, but this too was exceptionally difficult, the aircraft would not hold a wings level attitude and would persistently bank to one side and then the other. Although there was high altitude wind, this remainded more or less constant at cruise altitude.There were no engine issues and rudder trim was neutral.I have never encountered this issue when flying the FS2004 PMDG 737-8/900.Once at low altitude <15 000ft, control was normal to touch down.The following settings were in place at the time:All simualtion control realism settings were set to realistic (as per PMDG manual)Weather was set to download real-world conditions every 15 minutesI had intially failed to engage the 737 yaw-damper and realised this when I first noticed the control issue. Switching it on however, failed to normalise the situation.Has anyone had this issue before and if so can they suggest anything I should check?