P2715Q, iMac5K, flashes in sleep mode

I have a Dell P2715Q (REV 00A from October 2014) connected to an iMac 5K and it does the same thing. That is occasionally (every 5 to 10 mins perhaps) while in sleep mode it will flash on the screen the OSD "entering power saving mode", then go back to sleep. The other issue is sometimes it will not wake from sleep. I need to power it off at the outlet, wait a while then plug it back in. Toggling the power button on the front of the unit won't wake it either. I contacted Dell Support today and they're sending out a replacement unit. I'm wondering if the hardware revision has changed since I bought mine in Nov 2014? I am also seeing the display port issue on this model as well. Does anyone have a REV00B/2 or higher unit? Are they all the same?