I have been experimenting with the images in Photoshop and also going through the different gallery designs as I upload a sample image to incorporate it in a gallery. I will make up my images to 1564 px x 962 px, saving them at 200 dpi and making sure the sharpening is good. This is twice the pixel count for the gallery size.
This way, the image has more of the original pixel size and is not upsized too much when I complete it. My original pixel size is: 4368 px x 2912 px, so just to crop it 782 x 481 is upsizing it pixel wise (stretching it) to incorporate the image. It May sound confusing, but it seems the 200 dpi size is pretty good when the gallery downsizes to 782 x 481.
Upsizing is where you can really get pixelation or waviness and photo degradation. In other words, I originally uploaded 500 px wide images, and they really broke down in the gallery. I am using the Slideshow Dissolve. I guess this is the best to be done at this point.
I just thought this might help others with similar problems if your images look bad. If anyone else has thoughts on this, I'd like to hear them. I don't know what else to do.