first thing that comes to mind,is to make sure you were flashing the zip file and not the .exe utility
if you had downloaded the actual zip file from shipped roms,or extracted rom.zip from the utility yourself,next thing that comes to mind is where you on the eng hboot when running the ruu? it could be an issue with the eng hboot,or maybe even the google play hboot,installing the older images.
i think next time i would try installing 1.44 hboot first,then attempt to run the ruu.
for what its worth,you dont need to change your mid/cid in order to run the play ruu. you only need those things to be correct if you want the phone to be able to OTA,so you dont really need to keep changing them back and forth.
personally,the eng hboot scares me,id leave it well enuff alone as much as possible
other than that,id double check drivers,stuff running on the PC,usb cables,make sure youre not useing usb 3.0 or a hub,etc. the usually things that can screw with your adb/fastboot connections.