It involves the fuel quantity
DO NOT USE THE DEFAULT PAYLOAD AND FUEL MANAGER!!! You are only supposed to you the PMDG fuel and payload manager included wit the package. Try that.
The last flight I did was a complete failure because for some reason I extracted fuel from the tank closest to the tail while accelerating to M1. I passed M1 but my fuel extraction was so drastically wrong that the aircraft, to make a long story short, went out of control. I have much research to conduct to ensure I wont do it again but I'm pretty sure its because I began increasing the CofG by opening the wrong tanks. It wasn't even fuel that was feeding the engines as it was trim tanks but choosing the incorrect tank caused displacement that led to the acute pitching while under AP command. Out of the blue I went down to -10'000FPM and had to battle using a keyboard to get out of it. Its always been obvious to me to use the inner tail tank first but this time I didn't and the effect caused havoc. I stabilised but it wrecked my ascent so I aborted the flight.