GTX970 SLI GPU usage drops to <10% when playng games with triple monitor

I can't tell what happend, why this issue started.
Playing games in surround mode, with my 2 GTX970's SLI and my 3 Acer GD245HQ monitors was great for a long time.
All of a sudden (was it after the last Windows 10 upgrade?) FPS dropped after starting a game.
GPU usage 6-11% (come on GTX970's, you can do better)
Tried a few games to check if it was an isolated issue with one game.
But, no. Far Cry 4, Tomb Raider (2013), FIFA 17, Witcher 3 all not playable anymore.
Ok. Then tried to go back to older Nvidea drivers (used DDU in safe mode first).
Windowed mode, Borderless Windows mode, Full screen. nothing helped.
Turning of SLI. Superb graphics, but no surround of course.
Changed slots, changed monitor inputs, bought a new cooler on one of my cards.

Everything used to work very well but now:
FPS during gameplay (i.e. FIFA 17) 10fps, GPU usage 11% and 6%
When in windowed mode also 10fps, GPU usage 11% and 6%
But..............
After ALT TAB (in wondowed mode) The game is in the backgroud over 3 monitors , players running smoothly 115fps, GPU usage 97% and 99%
????????

My config today:
NVIDIA Systeeminformatierapport gecreëerd op: 10/24/2016 19:59:59
Systeemnaam: PC1
Besturingssysteem: Windows 10 Pro, 64-bit
Intel Core i&-5930K CPU @ 3.50GHZ
DirectX-versie: 12.0
GPU-processor: GeForce GTX 970
Stuurprogrammaversie: 375.63
Direct3D API versie: 12
Direct3D functieniveau: 12_1
CUDA-kernen: 1664
Kernklok: 1114 MHz
Geheugengegevenssnelheid: 7010 MHz
Geheugeninterface: 256-bit
Geheugenbandbreedte: 224.32 GB/s
Totaal beschikbaar grafisch geheugen: 20427 MB
Toegewezen videogeheugen: 4096 MB GDDR5
Videogeheugen systeem: 0 MB
Gedeeld systeemgeheugen: 16331 MB
Video BIOS-versie: 84.04.1F.00.2B
IRQ: Not used
Bus: PCI Express x16 Gen3
Apparaat-ID: 10DE 13C2 85081043
Onderdeelnummer: G401 0010
GPU-processor: GeForce GTX 970
Stuurprogrammaversie: 375.63
Direct3D API versie: 12
Direct3D functieniveau: 12_1
CUDA-kernen: 1664
Kernklok: 1114 MHz
Geheugengegevenssnelheid: 7010 MHz
Geheugeninterface: 256-bit
Geheugenbandbreedte: 224.32 GB/s
Totaal beschikbaar grafisch geheugen: 20427 MB
Toegewezen videogeheugen: 4096 MB GDDR5
Videogeheugen systeem: 0 MB
Gedeeld systeemgeheugen: 16331 MB
Video BIOS-versie: 84.04.1F.00.2B
IRQ: Not used
Bus: PCI Express x16 Gen3
Apparaat-ID: 10DE 13C2 85081043
Onderdeelnummer: G401 0010

[Onderdelen]

NvGFTrayPluginr.dll 3.0.7.34 NVIDIA GeForce Experience
NvGFTrayPlugin.dll 3.0.7.34 NVIDIA GeForce Experience
nvui.dll 8.17.13.7563 NVIDIA User Experience Driver Component
nvxdsync.exe 8.17.13.7563 NVIDIA User Experience Driver Component
nvxdplcy.dll 8.17.13.7563 NVIDIA User Experience Driver Component
nvxdbat.dll 8.17.13.7563 NVIDIA User Experience Driver Component
nvxdapix.dll 8.17.13.7563 NVIDIA User Experience Driver Component
NVCPL.DLL 8.17.13.7563 NVIDIA User Experience Driver Component
nvCplUIR.dll 8.1.910.0 NVIDIA Control Panel
nvCplUI.exe 8.1.910.0 NVIDIA Control Panel
nvWSSR.dll 6.14.13.7563 NVIDIA Workstation Server
nvWSS.dll 6.14.13.7563 NVIDIA Workstation Server
nvViTvSR.dll 6.14.13.7563 NVIDIA Video Server
nvViTvS.dll 6.14.13.7563 NVIDIA Video Server
NVSTVIEW.EXE 7.17.13.7563 NVIDIA 3D Vision Photo Viewer
NVSTTEST.EXE 7.17.13.7563 NVIDIA 3D Vision Test Application
NVSTRES.DLL 7.17.13.7563 NVIDIA 3D Vision Module
nvDispSR.dll 6.14.13.7563 NVIDIA Display Server
NVMCTRAY.DLL 8.17.13.7563 NVIDIA Media Center Library
nvDispS.dll 6.14.13.7563 NVIDIA Display Server
PhysX 09.16.0318 NVIDIA PhysX
NVCUDA.DLL 6.14.13.7563 NVIDIA CUDA 8.0.0 driver
nvGameSR.dll 6.14.13.7563 NVIDIA 3D Settings Server
nvGameS.dll 6.14.13.7563 NVIDIA 3D Settings Server

Is there anything I have not tried yet to get my cards running again?