There's something broken on your end. Transmissions don't even have the ability to break yet and the gear shifts aren't slow at all. You must have outdated mods installed, which isn't the game's fault. You're lucky the community here is so helpful. I know a lot of forums that would have insta-banned you after the first post. All changes made to the powertrain were also detailed at length in the devblog post for 0.8. I don't know what more you want.