I downloaded a few of the TDS 787-8, 9, and 10 from Simviation and they all suffered with the same problems. Flying nose down attitude, lifting mains before nose gear came off the ground, and extreme exaggerated nose down condition with full flaps on landing.
I talked with a guy with TDS tonight about a fix for it. He was not very happy that some things are being left out when installing a VC or another panel. In the panel folder, open panel config file. Look for the text that matches the regular text below and add the bold text under it. That should correct the problems I stated above. I tried it out on one of my 10 versions I just downloaded and it fixed it for me.
[VCockpit01]
size_mm=1024,1024
pixel_size=1024,1024
texture=$737_1
background_color=23,17,52
gauge01=B737_800!overhead_popup, 4,4,581,529
gauge02=B737_800!pfd, 6,536,260,260
gauge03=B737_800!trim_popup, 6,801,194,154
gauge04=B737_800!annunciator_speed_brake_armed, 6,961,51,28
gauge05=B737_800!annunciator_below_glideslope, 6,994,52,27
gauge06=B737_800!annunciator_panel_1, 64,961,132,40
gauge07=B737_800!mfd, 347,536,260,260
gauge08=B737_800!autopilot, 205,801,463,90
gauge09=B737_800!annunciator_panel_gear, 205,895,66,71
gauge10=B737_800!annunciator_le_flaps, 204,974,100,28
gauge11=B737_800!annunciator_auto_brake_disarm, 275,895,47,27
gauge12=B737_800!annunciator_anti_skid_inop, 275,925,37,27
gauge13=B737_800!flap_indicator, 308,960,59,59
gauge14=B737_800!compass, 325,895,91,62
gauge15=B737_800!compass, 370,960,50,50
gauge16=B737_800!clock, 424,896,105,105
gauge17=737-400!Transponder, 589,4,190,78
gauge18=737-400!Nav 2, 589,87,190,78
gauge19=737-400!Nav 1, 589,169,190,77
gauge20=737-400!Comm 2, 589,249,190,78
gauge21=737-400!Comm 1, 589,330,190,78
gauge22=737-400!Audio, 589,411,190,40
gauge23=737-400!ADF, 589,454,190,80
gauge24=B737_800!eicas, 704,541,260,260
gauge25=B737_800!adf_vor_backup, 757,908,104,105
gauge26=B737_800!attitude_backup, 533,896,104,105
gauge27=B737_800!alti_and_asi_backup, 641,909,103,103
gauge28=B737_800!efis_control_panel, 672,815,143,76
gauge29=B737_800!fmc, 783,2,236,370
gauge30=fs9gps!gps_500, 782,372,211,165
gauge31=B737_800!knob_n1_set, 828,825,43,46
gauge32=GPWS_Sound!dsd_xml_sound3, 0,0,,, ./sound/GPWS/Sound.ini
gauge33=rcb-gauges!GPWS3_3_Default, 613,751,82,31
[VCockpit02]
size_mm=512,512
pixel_size=512,512
texture=$Tds_ACU
background_color=0,0,0
gauge00=Tds780!Tds_AdvInit, 140,80,140,80
gauge01=Tds780!Tdsgearheight, 140,80,140,80
gauge02=Tds780!TdsNosegearsteerling, 140,80,140,80
gauge03=Tds780!Tdsgearretract, 140,80,140,80
gauge04=Tds780!TdsSpoiler, 140,80,140,80
gauge05=Tds780!TdsFlap, 140,80,140,80
gauge06=Tds780!TdsAileron, 140,80,140,80
gauge07=Tds780!TdsRudder_Elev, 140,80,140,80
gauge08=Tds780!TdsEngRev, 140,80,140,80
gauge09=Tds780!TdsWingflex, 140,80,140,80
gauge10=Tds780!TdsAUX, 140,80,140,80
gauge11=Tds780!TdsSEA, 140,80,140,80
gauge12=Tds780!Tdsflasher, 140,80,140,80
[VCockpit03]
size_mm=512,512
pixel_size=512,512
texture=$EXTANIMBASE
background_color=0,0,0
gauge00=EXT_TEXTURE_ANIM!EXTTEST, 0, 0, 512, 512
Rick