Kernel Panics...

Hi guys; I upgraded my Mac Pro 1.1 a while ago - and now been trying for quite some time to run Yosemite on it. The installation with SFOTT worked well, but I got some kernel panics from time to time...
A few days ago, it appeared again and I had enough... So I tried to fix it but I had no clue... so I turned to the macrumors forum and useful member gave me some hints - he came to the conclusion that my RAM is faulty/ or the 4 stock RAM modules are drawing too much power... so i removed the stock and than ran memtest - all fine, no errors...
However, a few hrs. later, my mac restarted because of a problem... now (for me) it seems like there is a prob. with the graphics card.. (but as I said, I have no idea (and the guy from macrumors is not responding...)

So I'm quite desperate right now and really help that one of you can help me..
My system:
2x Xeon X5355 CPU
now 8GB of RAM (tested & working)
1x 60GB Kingston SSD, 1TB WD Green GDD
Flashed Ati Radeon HD 5770 Graphics Card (1GB VRAM)

The error report:

I really hope someone knows a solution to this... greetings from Austria!