What I meant by Artlantis using 100% CPU on all 4 cores is that it is the only application that sustains 100% usage of CPU core for long periods of time. It happens throughout the rendering process. When working in preview window in Artlantis, CPU usage is like most programs showing a increase when regenerating the preview window and then returning to low percentage use. Obviously programs like Artlantis, rendering ones, use a lot more resources CPU and dGPU out of the rMBP and get the fans working. But so far on all other 3 15" rMBP with dGPU ( 2012/2013/2014) and iMacs (2013/2014 5K that I have AutoCAD LT 2014/15 perpetual license uses 8% to 30% (30% when regenerating viewports or model space) for the duration of the task and then idle if no command is active and I'm staring at the screen. In this new rMBP 15" with AMD 370M after 1h30m of working in AutoCAD 2015 LT monthly subscription I get 90 % tp 100% CPU usage constantly until I quit AutoCAD, and most of the times I have to force quit the app. I could be staring at the screen and it is still showing 100% CPU usage and the whole system shows 85ºC to 97ºC and fans constantly blowing.

I've tried safe boot + SMC and Pram reset and the problem persists.

I've tried using the laptop display only with dGPU AMD 370M and the problem persists.

I've tried connecting external display via mini display port to VGA to rule out HDMI trouble and the problem persists.

I'm going to use the Intel Iris Pro today with AutoCAD (I think it's the first rMBP 15" that I have the lets GFXstatusCard use the integrated Intel with the app all other switch to dGPU), and laptop display  and see if the problem persists.

If it doesn't work I'm going to reinstall the AutoCAD 2015 LT and see if the problem persists.