From my personal experience:
2 main ways you can kick faster.
Either you change your kicking technique to a method that is faster.
Either you keep your style, but train it to be faster with it.
Obviously, you can have a mix of those two.
You will loose some power, there's no way around it but it's up to you to adapt to something that suits you.
If you want to change your technique, it's a bit too complicate for me to give proper explanation through a forum. It mainly involve the snap at the knee, different angles, different use of the hips...
My suggestion is to go to a TKD school and explain that you just want to learn faster kicks for your MT. I was lucky enough to find an open minded TKD ITF guy, but i still had to do the Katas etc...
It may not be the faster way to learn, but it's probably the best way. But you have to keep in mind, it's a different style, with a different purpose. You will have to readapt what you learn there for MT.
My kicks are faster, my reaction time is faster, my distance management is better, i see more openings, i have more kicking tools, better flexibility, less telegraphed strikes, more feints, and learned to use both my legs, and both stances... All of those are making me a faster athlete in general.
I think that after the first 2 years of cross training, i started to see a real difference. I understand if it's seems a long time, but for me it was well worth it.
Probably some Karate schools can suit your needs... But I'm not familiar enough with them to suggest one.
Now if you want to keep your style, and just do some exercises, that's what I've got:
-Flexibility has a huge role with it. It will sound bizarre, but when your mind knows it safe to kick at a certain hight without risking injury, it allows you to bypass some security measures it has for you to not get hurt. Subconsciously limiting the speed is one of them. That's why it's easier to throw full extended punches when shadow boxing, but when it's come to kicks, and there is no target, you either slow down, or don't fully extended your legs...
-Work on your balance. Learn how your body react when throwing a fast kick in different situations. If you miss your target, or if you are countered... It's not the same when you strike harder but slower...
-You said you started kicking the heavy bag with speed in mind instead of power. I can guarantee you that is the first and best method to train faster kicks... But it's a long road. You must change your training mentality from power to speed. Not only on the bags, but on the pads, and while shadowing...
-Shadow boxing at full speed with kicks is fakin hard. For MT, our roundhouse go through the target, so we must spin 360° every time we kick fast... After a few kicks, it's not really doable for long. But you can change you angle, make it a more upward movement, and that will limit the need to rotate fully... But again, it's something that might change your technique.
You might need to "relearn" that instead of spinning if missing the target, to put your kicking leg in front of you, while switching position.
Another way is to just start the movement fast, without going through it with same speed, or even fully extend the legs.
-Have a partner hold boxing mitts for you. Not MT kicking pao. Regular small boxing mitts for punches. Usually we use just one in TKD. Have your partner showing it suddenly, at different high, regular or switch. You have to kick it as fast as possible (with the instep), but try to keep a good technique. That will improve your kicking speed and reaction time.
-Resistance bands are a very a good help.
-Drills for explosiveness, instead of just muscling up you legs... Sprints, fast double jumps from squad position etc...
-My opinion is that speed drills should be done fresh. There is no point of working your muscle memory for speed, when you're dead tired and slower than a dead sloth.
-I don't find that you have a slow kick, just some time your repositioning. So keep that in mind when you drill kicks, that you have to put your leg back as fast as it was raised...
You will have to readapt your whole training with speed in mind instead of power. And it might take some time. But that doesn't mean you will loose power when you need it. You wont suddenly forget how to kick hard. You just have to find the right balance for you, learn to have different types of kicks for different needs...fast vs power, or a mix of them....
