Unless you have Nascar-level skills, a modern automatic is going to be more efficient and better at successfully changing gears as needed than you are. The only reason to have a manual transmission these days is ego.
My experience with modern automatics is that they are dogshit and constantly changing gears at times that I don't need it to. Just a bit of a hill? Pull it out of overdrive. Very slightly accelerate on the highway? Put it in 2nd gear! Even really nice vehicles like the Toyota 4Runner have absolutely terrible auto transmissions. Just ruins the experience for me.