Upgrade mac pro 4.1 to 5.1 does not work (it just reboot normally)

In my quest to update my mac pro 2009 (4.1), I did encounter a roadblock, since the last OS that I can run on 4.1 is 10.11. Now; I found a method to flash the machine so it becomes a 5.1; which allow me to install up to Mojave I believe. The problem is that after following the instructions, the machine won't update. This is what I did - mount the firmware update DMG and run the app, it create a ram disk on desktop - Once done, it ask me to shut down the computer and restart it. - I restart as per instructions; holding the button until the light flash and the machine beep, but it just boot in the current os, and no update is done I did check the following - my 4.1 mac has the latest firmware available officially from Apple - I have the original GT120 that came with it, in the bottom slot (not the 16x, since that card is garbage); also the only other devices plugged in, beside the mouse and keyboard are 2 extra hard drives. So far, after reading forums and tons of huge posts, I found no way to solve my problem. So I hope anyone here has experience with the procedure and can point me to the right solution. Once I get this done, my second step will be to go for High sierra or Mojave, and then try to install windows via bootcamp, but one step at time.