Hi Lucien,
No idea why your paint looks darker, but I believe you. I have used other products before that made the paint look darker - off the top of my head, I recall Meguair's show car glaze did this.
AIO and SG are great products in my opinion. I use them myself and have been very happy overall with their results. They last for a very long time, are relatively easy to use, and make paint look fantastic (especially darker colors).
However, in my experience, they are relatively poor in dealing with swirls and scratches. Therefore, if you are going to keep using the Klasse combo, I would advise you to be extra careful about how you wash your truck - clean microfiber towels only, and rinse them before putting them back into the wash bucket. How you dry is also important. Prevent those swirls before they happen, because Klasse will not take them away.
Also, if you have not yet discovered the joys of detailing clay, you should give it a try. It really is not difficult, and the results will amaze you.