If your 2013-model Mac Pro is having video issues, Apple may be ready to fix the problem for free. The company has a new hardware repair program in place to deal with the issue, but you'll have to ask because it isn't being advertised.
Apple fixing Mac Pro video issue for free
Apple will replace the graphics cards in affected Mac Pro models made between February 8th and April 11th, 2015, at no cost. Symptoms to look for include no video or distorted video, system instability or freezing, unexpected restarts or shutdowns, and failure to start up.
According to Apple internal documents obtained by MacRumors, the issues are cropping up in the AMD FirePro D500 and FirePro D700 video cards. You'll need to make an appointment at your Apple Store Genius Bar to schedule the repair, and it'll take between three and five days to complete.