Behr does a lot of advertising and convinces folks that it's a great paint, it's not. It is inexpensive and you can get it on a Friday night or Sunday morning. I'm using some of their exterior premium plus and have no complaints but it is a two coat minimum paint. The exterior gives you plenty of time. I have used some interior acrylics that are like marshmallow fluff. My painter friend likes to say, you have to be a good painter to use the stuff, forget it if you are an amateur.
There can be a lot to painting. The type of brush you use, how you load it, what angle you hold it at to apply and what angle you tip off with. A brush can be similar to a trowel. Purdy is now listing their brushes as soft, firm, etc. With a thick paint, you may want a stiffer brush. Still, it's a matter of laying down, blending and tipping off with a minimum of strokes, you can't overwork it or go back.
I'm doing some interior paneled doors with an oil based that tacks quickly, I'm using a brush in the corners and a paint pad for the rest. I'm getting great results, no marks, even application and it's real fast, although, you go very slow with the pad. The throw away styrofoam ones are less than $3, try one of those.