Reversing a bad (non cummins) tune

[DVT873]

APC, it is an international medium-duty DT engine. Not a Cummins. This post by Rawze sort of answers my question, I think. https://rawze.com/forums/showthread.php?tid=10576

My question is: when somebody "tunes" an engine, does just reflashing it return it to stock? Or did they f$%k with settings that a stock reflash won't correct? I have 2 trucks in my area with this engine that some "master mind" put delete tunes in. Both ran great for about 3 weeks, then went into what feels like a limp mode. No codes with a scanner or International software. One fleet wants it back to stock. I can reflash it back to stock, but will that be enough?

This particular ECM/ACM setup is twitchy. Bench reflash is best. ECM/ACM access sucks because there are several body-related hydraulic hoses in front of it.

I am trying to figure out the best way to go. Replacing the ECM is a possibility.