[Matt Cramer]

I used an MS3-Pro on my truck. It was definite overkill for a stock 4.8, but I was using it to develop a custom wiring harness. Here's my take on what situations a stock ECU would be a good fit for, and what ones would call for a standalone.

Stock engine? Stock ECU makes perfect sense here; you don't really want much in the way of tunability.

A couple minor bolt ons or a cam swap? It shouldn't be too hard to adjust the stock ECU for this.

Forced induction or a serious naturally aspirated build? OK, this is starting to get to the point where you will want to look at standalones. You might be able to tune a stock ECU to run this. However, standalone ECUs are often a bit simpler to tune under boost (no weird MAF trickery, for example) and give you access to features like the individual cylinder trim tables. A lot of those settings in a stock ECU are hard to access and often wrong for a turbo or all out build. You could add more fuel across the board to compensate for a lean cylinder, but that would leave power on the table.

Another good reason to start looking at standalones is if your build calls for a lot of black boxes for features a stock ECU can't easily do - standalones have a lot of race features as standard equipment. I've heard of tricks to sort of get boost control out of a stock ECU, for example, but not to make one do closed loop boost control that ramps in the boost on a timer after you release a two step rev limiter, or ones that will let you creep forward on a trans brake. (Stock ECU gurus, feel free to chime in if there is a trick to do this.)