Strange color negatives among good ones

If I may continue this thread with another problem concerning film, here goes.....I don't seem to be able to get quality focused images at over 50% and they have considerable grain and other artifacts especially in the sky. I have tried several scanning ppi settings from 300 to 2400+ with adjustment for target size of the image, but with the same poor effects. I get bigger images, but not better. I thought I would get better enlargements from film than from my digital cameras. My scanner is an Epson Perfection V500 Photo. I do not use any scanner enhancement. My images are good in smaller sizes. Thanks for your continued help.

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Christian Amateur Photographer