Ok so I'm just going to straight say it as it is. the stunlock system is garbage, 2 zombies come onto you, you might as well just exit the save because your not getting out of that without bites. I've had it happen repeatedly and I'm one of the "zomboid pro's" BUT I've come up with a simple solution.
Link stun locks to fitness and strength:
for example trips and fence lunges are handled by Fitness while zombie attacks (where you push them off of you) are handled by strength, higher the strength farther and quicker you push a zombie off of you, and higher fitness means you get up quicker. I'd also suggest a stun on the zombies as well. because the animation for pushing a zed is just as long as it takes for a zombie to stop falling back and come back (you'll push them away just to have the same zombie on top of you) perhaps make the zombie stagger and realign itself and THEN start moving to you.
please think about this as those stunlocks are not at all balanced. they end more saves just because there is 2 zombies on both sides of you and you physically cannot escape. that is not a fair death. which you could say "zomboid doesn't give you a hand" which is TRUE, but balance is also important when making a game like zomboid