Meljet with PSS cockpit - FMC funny behaviour and stall after TO!!!!

I have installed the Meljet v1.0 (Air France repaint) with the PSS 777 panel, using one of the merge files from this forum.Although I have done a zillion takeoffs in FS, including many with a merged PSS/Meljet 744, I cannot get this one to take off properly. The problem is that to get the plane off the ground I either have to pitch the nose up a lot (with "default" trim set at 8.0) OR use a lot of trim (around 8.5) and only a little pitch up. In both cases the plane quickly looses speed right after take off and stalls somewhere around 400-700 ft AGL. In the beginning I thought this had to do with my trim/pirch settings, but then I also observed something else:on the VNAV page of the FMC the reading is "ACT 280 CLB" until shortly before rotate, and then suddenly changes to "ACT 180 CLB". Also, when up in the air, just for the diagnostics of it I have pressed the speed button so as to climb with V/S rather than VNAV, and the speed indication was "10"!!! Also, on climb, the AP engages the LNAV mode, but not the VNAV mode.So something seems to be happening there causing the aircraft wanting to go to lower speeds, I just don't know what.Could someone give me a hint on i) which trim and pitch to use and maybe how to adjust it after T/Oii) what could be wrong with the speed settingsI am using the following config:- TOW 231,000 kgs (approx. 509,000 lbs)- flaps 15- VR 139 kn- FD, ATHR, VNAV, LNAV switched on- TO/GA pressed for throttle- FMC properly programmed with a SID, the route and all the INIT REF settingsSo what can I do??? Really desperate..