Hi @code600, I tried the same thing today, flashing a MBP2014 with 2015 NVME drivers. I followed the steps outlined here: https://forums.macrumors.com/thread...e.2034976/page-54?post=26102169#post-26102169
Dosdudes ROMTool confirmed the flash, but rechecking with UEFITool suggests, that nothing got flashed. Even the checksum did not change. (My System is running on a 960GB JetDrive 'TS960GJDM850' on a MacBookPro11,3 with OSX10.13.6)
Any hints on how you did this?
I first took a 2015 macbook, updated it to the latest firmware. Dumped the firmware on my computer using the TL866II programmer. Opened the firmware with UEFITool and looked for the file that starts with 51116915, right click on it and click Extract As Is and save it(I noticed on the newer UEFITool for some reason you can't extract anymore so use older version). Then I dumped the firmware from the 2013 macbook on my computer. Opened it with UEFITool then found the same 51116915 file and right click, replace as is, locate the previous file that I extracted, then save the rom file. Hook up the programmer, open the file and flash it. You don't need a 2015 macbook you can extract the nvme file from the OS installer.
If you are using Dosdudes ROMTool, all it does is just read your original rom file and it can write a rom file to your macbook as well, But you will need to use the UEFITool afterwards to inject the NVME file (the one you extract using UEFITool from a OS installer) then use the Dosdudes ROMTool to flash the saved ROM to your macbook. I would recommend getting a SPI flash programmer and also a SOP8 adapter clip so you don't have to desolder EFI chip, all you would need to do is add additional 3.3V to 1 of the power pins to power on the chip. Doing it using Disdudes ROMTool doesn't require any of the programmers but if something goes wrong then your macbook will not function anymore and then you would need to buy the programmer to fix it