I have a buddy from work that just got an 07.5 LMM and did a DPF delete on his truck. I havent downloaded his stock tune to see what the OS is. I have a nice tow tunes with DPF delete that my buddy Reece built for my truck with the original OS before they did the recall for non starting issues. I guess my question is can I do a full system reflash to the OS I have and than work on building him a new tune from his stock tune.

Not heard of anyone doing a full flash of say the older OS on a newer OS ECM and not have a problem. Should work fine. Scripting will get you setup quickly. Got the original OS stock tune and your modified tune of the same os then make a script and apply the script to his stock tune OS. Done. Recommend fully updated to the latest public release of EFILive on thier website. Has some table fixes if you have not updated in a while.

Brian

As Brian has said, there is no problem with re-flashing the old OS back into the ECM, but a smarter way to do it would be to build scripts and keep the new OS.

From memory, most of the professional tuners prefer the later LMM OS to the earlier one.

Cheers
Cindy