Laptop over heating round 2!

So a little over a year ago my Alienware MX17 R3 was having crashing/overheating problems. It quickly escalated until my pc died. I had to ship it off to dell and hand them $430. After that I renewed my warranty which was around $300. Dell replaced the mother board, thermal paste, and both fans. A year has passed and I didn't renew my my warranty simply because I forgot.

This time around my HDD is fine, but any time I open a program that renders anything 3D all 4 cores of my cpu hit about 160F and my video card goes over 190F that's with my targus cooling mat(info. from speccy and speedfan). If I'm running a game the fps drop rapidly to 0. The screen goes black and the audio loops on the last bit of sound until my laptop restarts.

I've ran the built in boot diagnostics and everything passed including the test for both fans. I ran Dell's online diagnostics which has a wireframe tests, a light rendering tests, and a full 3D environment test the laptop passedconfused). However, the problem persists so I cleaned all the dust out of the vents, heat sinks, and fans; removed all the thermal paste(most of which was dried) replaced it with artic thermal paste; Cleaned all the contacts with alcohol; set windows 7 to best performance (because why not?); uninstalled a great deal of software; ran several anti-virus/malware programs just in case. Now everything sits at a lower running temperature, and I can run games for a slightly longer time before the laptop crashes.

If the laptop isn't plugged in there is no problems. I turned core parking off and have to run everything on a lower setting but it doesn't crash. My battery life is so short I can't play anything long. The moment its plugged back up it crashes. If the battery is out and it's plugged up it crashes. The only discernible difference while its plugged up is that turbo-boost on my cpu kicks in, the power flowing to my laptop, and increased heat from the power.

Because the crash doesn't occur unless I'm running a 3D program while my laptop is plugged up, and because Dell previously replaced the mother board I'm torn between replacing the graphics card, or sending it to them to get the mother board replaced. What something I can do to determine indefinitely which it is? Also any advice would be greatly appreciated! Thanks in advance.

System Info:
Processor:
Intel Core i7 2860QM

Memory(RAM):
8 GBs of DDR3

Hard Drive:
750 GB

Video Card:
Nvidia Geforce GTX 580M

Mother Board:
Alienware M17xR3

LCD Panel:
17.3 Inch WideFHD 1920x1080 120HZ

Network Card:
Killer Wireless-N 1103

Post from a year ago.

P.S. once I get it up and running again its being sold and replaced entirely. I can't upgrade the graphics card in it so I'm just going to get a better laptop altogether.