I have a very similar problem as outlined here. Several fresh installations of 10.12.3 as well as the beta did not fix the sudden restarts.

I'm using a Mid 2014 MacBook Pro Retina with dedicated GPU.

Do you see some things to try?

• several reinstallations did not help (also the reset installation)
• hardware test does not report failures
• no problems with SSD disk utility
• already reset NVRAM
• the problem does not seem to apprear in safe mode (but safe mode ist not really a mode to work in)

Feb 28 18:41:37.190986 +0100 000001.269937 Brcm4360<D>[1794] [0xbfc5df44490844e7][1][0] CoreCapture:reinit@35=PCIErr-Status{LnkSt=10110143,DevSt=123C10,VID=14E4,DID=43A0,STS_CMD=8100406,BAR0=C1A00004,BAR1=C1800004,US=8000,CS=1
Feb 28 18:41:37.190987 +0100 000001.269938 Brcm4360<D>[1795] [0xbfc5df44490844e7][1][0] Skip capture: Capture:0, wl_powercycle_inprogress:1
Feb 28 18:41:37.190989 +0100 000001.269940 Brcm4360<D>[1796] [0xbfc5df44490844e7][1][0] Fatal Error - Initiate powercycle 
Feb 28 18:41:37.190991 +0100 000001.269942 Brcm4360<D>[1797] [0xbfc5df44490844e7][1][0] wl_fault_powercycle: thread_call_enter1 - Power Thread scheduled
Feb 28 18:41:37.190992 +0100 000001.269943 Brcm4360<D>[1798] [0xbfc5df44490844e7][1][0] Perform hard reset, skip core init
Feb 28 18:41:37.190993 +0100 000001.269944 Brcm4360<D>[1799] [0xbfc5df44490844e7][1][0] AirPort_Brcm43xx::syncPowerState: Device in bad state after wakeup - err:-1
Feb 28 18:41:37.190995 +0100 000001.269946 Brcm4360<D>[1800] [0xbfc5df44490844e7][1][0] AirPort_Brcm43xx::syncPowerState: Device in bad state after wakeup - err:-1
Feb 28 18:41:37.190998 +0100 000001.269949 Brcm4360<D>[1801] [0xbfc5df44490844e7][1][0] AirPort_Brcm43xx::syncPowerState: returned: powerStateOrdinal = 2, callback[2] systemWoke[0] _powerSleep[0] _powerState[2]
Feb 28 18:41:37.191000 +0100 000001.269951 Brcm4360<D>[1802] [0xbfc5df44490844e7][0][0] AirPort_Brcm43xx::setPowerState: powerStateOrdinal = 2, ACK'ing.
Feb 28 18:41:37.191004 +0100 000001.269955 Brcm4360<D>[1803] [0xbfc5df44490844e7][1][0] powerCycleOffOnThread - Start Powercycle..., _powerOffOnDelayms[ 300]
Feb 28 18:41:37.191009 +0100 000001.269959 Brcm4360<D>[1804] [0xbfc5df44490844e7][1][0] powerCycleOffOnThread: M_DRIVER_AVAILABLE:0, event:0, reason:e0823801, sub_reason:e3ff8d23, minor_reason:0, reasonString:reinit@35=PCIErr-Status{LnkSt=10110143,DevSt=123C10,VID=14E4,DI
Feb 28 18:41:37.191011 +0100 000001.269962 Brcm4360<D>[1805] [0xbfc5df44490844e7][1][0] AirPort_Brcm43xx::powerCycleOffOnThread: calling setPOWER(OFF)
Feb 28 18:41:37.191013 +0100 000001.269964 Brcm4360<D>[1806] [0xbfc5df44490844e7][1][0] AirPort_Brcm43xx::setPOWER(): >>>> _powerState[2] _lastUserRequestedPowerState[2] _systemSleeping[0] _powerOffInProgress[0] _powerOffThreadRequest[1], _powerSleep[0] pid[0]'kernel_task'
Feb 28 18:41:37.191015 +0100 000001.269966 Brcm4360<D>[1807] [0xbfc5df44490844e7][1][0] wl0: setPOWER: num_radios[3]  power_state(0:0  1:0  2:0  3:0)
Feb 28 18:41:37.191017 +0100 000001.269968 Brcm4360<D>[1808] [0xbfc5df44490844e7][1][0] AirPort_Brcm43xx::setPOWER(OFF): _powerState[2] _lastUserRequestedPowerState[2] _systemSleeping[0] _powerOffInProgress[0] _powerOffThreadRequest[1] selfpid[0] inprogress[0]
Feb 28 18:41:37.191059 +0100 000001.270010 Brcm4360<D>[1809] [0xbfc5df44490844e7][1][0] wlIoctl: wlc_ioctl called with cmd 118 returned error -26
Feb 28 18:41:37.191061 +0100 000001.270012 Brcm4360<D>[1810] [0xbfc5df44490844e7][1][0] wl0: setAP: err setting ioctl WLC_SET_AP to 0, err -26 "Not Permitted"
Feb 28 18:41:37.191062 +0100 000001.270013 Brcm4360<D>[1811] [0xbfc5df44490844e7][1][0] AirPort_Brcm43xx::setPOWER(OFF): calling changePowerStateToPriv( PS_INDEX_DOZE )
Feb 28 18:41:37.191070 +0100 000001.270021 Brcm4360<D>[1812] [0xbfc5df444908497f][0][0] AirPort_Brcm43xx::powerStateDidChangeTo: 2, timestamp[0x0000000000136103] calendartime[0x0005499ab530609c]

and

Feb 28 18:41:37.182899 +0100 000001.261850 Brcm4360<D>[288] [0xbfc5df444908497f][0][0] AirPort_Brcm43xx::powerStateWillChangeTo: 2, ACK'ing
Feb 28 18:41:37.182909 +0100 000001.261860 Brcm4360<D>[289] [0xbfc5df44490844e7][0][0] AirPort_Brcm43xx::setPowerState: Called powerStateOrdinal = 2, timestamp[0x0000000000134122] calendartime[0x0005499ab53040bb]
Feb 28 18:41:37.182911 +0100 000001.261862 Brcm4360<D>[290] [0xbfc5df44490844e7][1][0] AirPort_Brcm43xx::syncPowerState: powerStateOrdinal = 2, callback[2]systemWoke[0] _powerSleep[0] _powerState[0] _down[0] _up[0] osh[0xbfc5df44491fd42f]
Feb 28 18:41:37.182963 +0100 000001.261914 Brcm4360<D>[291] [0xbfc5df44490844e7][1][0] wlc_verify_d3_exit: AER_UC_NON_FATAL: STS:00008000, SERV:FFF9DFCF
Feb 28 18:41:37.182967 +0100 000001.261918 Brcm4360<D>[292] [0xbfc5df44490844e7][1][0] wlc_verify_d3_exit: PCI_CFG_AER_CORR_STS: STS:00002000
Feb 28 18:41:37.182975 +0100 000001.261926 Brcm4360<D>[293] [0xbfc5df44490844e7][1][0] wlc_verify_d3_exit: PCI_CFG_STAT:00000810
Feb 28 18:41:37.182977 +0100 000001.261928 Brcm4360<D>[294] [0xbfc5df44490844e7][1][0] wl0: fatal error, reinitializing, total count of reinit's[1], @'wlc_verify_d3_exit':57164
Feb 28 18:41:37.182985 +0100 000001.261936 Brcm4360<D>[295] [0xbfc5df44490844e7][1][0] wl0: 802.11 reinit reason[35], count[1]
Feb 28 18:41:37.183053 +0100 000001.262004 Brcm4360<D>[296] [0xbfc5df44490844e7][1][0] wl_fatal_error: fatal error within 450 ms, limit:4000 ms. currentRetryCnt:1, max:3
Feb 28 18:41:37.183055 +0100 000001.262006 Brcm4360<D>[297] [0xbfc5df44490844e7][1][0] AirPort_Brcm43xx::setPowerCycleInProgress: state [0] -> [1], name['wl_fatal_error'] id[31094]
Feb 28 18:41:37.183057 +0100 000001.262008 Brcm4360<D>[298] [0xbfc5df44490844e7][1][0] AirPort_Brcm43xx::setPowerCycleInProgress: _up[0] _down[0] _powerSleep[0] _powerState[0] _powerCycleThreadWaiting[0] _powerOffOnThreadBlockedForWake[0] _powerCycleOffOnThreadRunning[0]
Feb 28 18:41:37.183064 +0100 000001.262014 Brcm4360<D>[299] [0xbfc5df44490844e7][1][0] Log system state... : reinit@35=PCIErr-Status{LnkSt=10110143,DevSt=123C10,VID=14E4,DID=43A0,STS_CMD=8100406,BAR0=C1A00004,BAR1=C1800004,US=8000,CS=1
Feb 28 18:41:37.183066 +0100 000001.262017 Brcm4360<D>[300] [0xbfc5df44490844e7][1][0] wl0: Dec 22 2016 23:34:31 version 7.21.171.68 (TOB) (r667042)(P2P)

Feb 28 18:41:37.183068 +0100 000001.262019 Brcm4360<D>[301] [0xbfc5df44490844e7][1][0] KMOD info(name: 'com.apple.driver.AirPort.Brcm4360' version['1130.3.1a5'] 

edit

No panics reported, only diagnostics. However this link contains the full output for the AirPort crash mentioned above.

To clarify: the notebook will either freeze and then shutdown or go to black and shutdown. It will not restart automatically. And I do not see the grey screen of death indicating a kernel panic.