I have a 2015 15" MBP fully maxed out - GPU, i7, 1TB, running fresh High Sierra install.
I've been having a ton of problems with it throttling (Intel SpeedStep kicking in) even under less than heavy usage. Recently the screen started freaking out, and I managed to capture video of it on my phone (imagine the image you're seeing with the various distorted parts flashing in and out).
The machine is covered by AppleCare. Took it the Apple Store, where it had problems booting some of their diagnostics, they sent it to a service center (along with my video caps). A week later they sent it back saying they couldn't reproduce the problem, sorry.
I'm fairly convinced this is a hardware/GPU issue - anyone ever seen this kind of distortion before?
I'd like to gather some more data points from others before going back to Apple.