It might not be the RGH mod, have you thoroughly checked the board for damage? Or a loose connection on one of the wires.
To test if the xbox is fine, flash back to stock nand, de-solder GND, then boot it should boot ok and boot the original Dash. If you get RROD something is wrong somewhere.
I would of thought you would not need to cut any wires as you had it working already. It could be you just need a capacitor between GND and CPU_PLL_BYPASS normally a 68nf or 100nf works well.
Photos and more info on your exact application of the RGH mod would help.
Post logs, list programs used, timings used etc etc.
Also dont just focus on the Xbox look at the chip too, resistors and other components can get damaged.
My TX coolrunner Rev b I installed last week just stopped working all of a sudden, I then noticed the 22k resistor was only reading 3.5k, so I replaced it and then it Glitched perfectly after that.