Be aware that in order to play back 4K video, you must have a pretty powerful computer with up-to-date software and a decent video card. "Choppy" video is caused by the inability of the computer to keep up with the video processing, so it skips frames and becomes unwatchable.
Take your video and watch it on a better computer. Or shoot in a lower resolution and see if your video doesn't display properly on your current computer. If a different computer (more powerful and capable of processing 4K video) shows it fine, then it's the computer. If even the best computer doesn't display the 4K video well, then it's the write speed of your SD card. If it plays fine on your computer hard drive but not on your microSD card with a USB drive, then it's the read speed of your USB or microSD slot. Make sure your'e using a USB 3.0 reader or a high speed microSD slot on your computer.