Just a quick question or two. Would you be okay doing your own tech works and are you already happy with the performance? Also which type of M4?
If so would probably look at the calibre of lipo you are using and then see about a mosfet. Those would be two areas to explore to deal with semi lock-up.
If your already using a decent spec lipo, then something like a Gate Titan NGRS model would probably help. If you do choose to go for one, make sure you get the correctly wired model.
E.g. Rear wired for the Sopmod, Front wired for Socom.