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It's probably not an issue with roller cover selection, but more of a wet edge problem. The goal should be to have the entire piece wet with paint at the same time so that it will all dry down evenly and together. Of course this is easier to do on smaller pieces. What is happening is that you work on one section and it is already too dry by the time you work on the next section and you are rolling back into that first section which is already too dry. So, you pull off some paint there that is really starting to set up already and that's why you have the dead spots there. I would try to add some extender to the paint to give it a longer open time and then roll all the way from one end to the other and don't stop or take any breaks between dips of paint. Modern day paints are very sensitive and fast drying and even letting an edge sit for 20 seconds may be too long. Also, the brand Behr probably isn't the best and the color is also a factor. Blacks are just tough to get to look nice unless it is sprayed or the product is oil based. Good luck!

You are rolling until the rollers are too dry, and spreading it too thin, so you have an edge problem.

Use a wider roller, and DO NOT roll until you hear that "frying bacon" sound of a dry roller. Roll it fast, and use ample amounts of paint.