AMD Radeon HD 6750M, Early 2011 MBP, 10.9.4 Problems

Question

Hello,
Ever since 10.9.3 update I have a serious problem with my Early 2011 MBP with AMD Radeon HD 6750M card.
First my configuration:
MBP 2.2 GHz Intel Core i7 (Macbook Pro 8,2)
16 GB RAM
512 GB Sandisk SSD and 750 Stock HDD
AMD Radeon HD 6750M and Intel HD Graphics 3000
OS X 10.9.4
I'm usually using my MBP with external display with a resolution of 1920x1080. The display is connected via DVI to Mini Display Port adapter. When I connect the external display, my MBP switches to the AMD card. Here's where the problems begin. If I'm using Davinci Resolve, Capture One Pro or any other software (that I use regularly) that uses the GPU extensively, the cpu usage will rise, the computer will start to feel sluggish and my productivity almost becomes none because even the simplest tasks such as opening another tab in firefox or safari takes anywhere between 1-3 sec. When the computer starts doing that, I cannot play a simple HD video at native fps and the whole machine basically becomes too expensive paper weight. The strange thing is that even after I quit all programs, the system cpu usage continues to be high, around 50% with kernel_task being the star using all this cpu and it keeps using all of this cpu forever, at least until i shut it down or disconnect the external display and manage to make it switch to the internal Intel gpu.
The problem started after istalling the 10.9.3 update and it's still there with the 10.9.4 update. I even formatted the computer and reinstalled everything but the problem still persists.
I haven't experienced anything like this on 10.9.2 and the machine was actually quite fast before that. Now, I have too expensive paper weight on my desk.
Since the problem is very specific, I doubt many users will complain and I doubt Apple will ever do anything to fix it, at least until hopefully the new drivers in 10.10 fix the issue hopefully.
My question is:
1. Has anyone else experienced this and managed to solve the problem?
2. How can I downgrade to 10.9.2? I don't have time machine backup but i have bootable usb with 10.9.2. Will it help?
All best,
Goran

Answer 1

When you have the problem, note the exact time: hour, minute, second.   
These instructions must be carried out as an administrator. If you have only one user account, you are the administrator.
☞ Launch the Console application in any of the following ways:
☞ Enter the first few letters of its name into a Spotlight search. Select it in the results (it should be at the top.)
☞ In the Finder, select Go ▹ Utilities from the menu bar, or press the key combination shift-command-U. The application is in the folder that opens.
Open LaunchPad. Click Utilities, then Console in the icon grid.
The title of the Console window should be All Messages. If it isn't, select
          SYSTEM LOG QUERIES ▹ All Messages
from the log list on the left. If you don't see that list, select
          View ▹ Show Log List
from the menu bar at the top of the screen.
Each message in the log begins with the date and time when it was entered. Scroll back to the time you noted above. Select the messages entered from then until the end of the episode, or until they start to repeat, whichever comes first. Copy the messages to the Clipboard by pressing the key combination command-C. Paste into a reply to this message by pressing command-V.
The log contains a vast amount of information, almost all of it useless for solving any particular problem. When posting a log extract, be selective. A few dozen lines are almost always more than enough.
Please don't indiscriminately dump thousands of lines from the log into this discussion.
Please don't post screenshots of log messages—post the text.
Some private information, such as your name, may appear in the log. Anonymize before posting.