Thoughts on power adding harnesses?

[Dietzster]

I know what you're thinking and before everyone rains down with their opinion, I would like to hear from people who have good or bad experiences with them and how they have worked out in the long term. I have a 2007 ISM500 CM875 in my motorhome. For what it is used for a few times per year {part of post removed by rawze}, I have never wanted to add more power or anything to it, however I wouldn't mind trying a few things to improve fuel mileage. I did have some EGR issues a few years ago with it and decided to try The Ugly Fix on it and it has been working {part of post removed by rawze} since then.

I'm typically not a fan of cheap mods like this {part of post removed by rawze}. Like the {part of post removed by rawze}, there is not alot of reliable info online (most people seem to have zero clue what they are talking about, lol) but thought for the cost it might be worth a try. Again, only being used a handful of times per year I'm not going to spend the money on a full tune from someone I don't trust as ISM tuning seems rare or non existent at most shops and I'm happy with current power levels, just want to try and tweak some mileage out of it if possible. Not opposed to making my own harness if anyone has proper part list for this application, most harnesses online seem to be only for ISX, does anyone know if they are compatible with ISM?

Won't make any stupid decisions on this without having all the facts first, lol. Appreciate it, thanks everyone!