I will throw my experiance in here, and see if you can relate, for this sounds like me just a few weeks ago.
I have a 4 yr old OTTB. Cowboy was being quite the stinker almost every day - Using a smooth dee, I had to PULL on his mouth, give, PULL, give, PULL to get him to come down to anything below a canter. Another scenario of the same proportion from the trot. So I got a slow twist.
This is a HARSH bit if used incorrectly. You need to learn that you cannot pull half as hard on this bit as you do in your normal untill you need to. The object is to make him give, and understand respect for the bit, NOT to make him listen and regret anything other.
THIS IS IMPORTANT - After 2 sessions of the slow twist, I took it off. Put him in a full cheek french link, and we have had no problems since. You don't just throw a hard bit in his mouth and say wahoo! You use it for just a bit to make him understand, 'woah, I shouldn't pull on bits,' then you reward him and take. It. Out.