Aircraft: 757-200 Captain Pro Pack (FS9) v2.2

Is it just me? This aircraft becomes unstable on wide LNAV turns (i.e. 30-degree or more): During the turns, it has trouble maintaing ALT and speed, it descends and climbs at 500FPM+ rates trying to chase the A/P selected ALT and the engines rev up and down to try to maintain speed. I am an experienced FSimmer flying by the book. Any ideas?

Thank you,

Kerke