I rolled both Quins LTK Monk and Bigdadaddydens Garg' Witch Doctor this season. Both are insane but I found keeping up the sweeping wind annoying on the Monk. My WD however is eating through content, running through a t12 rift with 4 other players, I weren't giving them a chance to kill stuff
Yeah I had the same problem with the LTK monk. At first, I found my sweeping wind stacks were dropping nearly all the time and I actually started to dislike the build but then I watched Quinn's video on his LTK build and picked up a few pointers which makes it much easier.
1) Get max Crit Chance through items and paragon, max is 53.50% iirc. The more crit the more likely the sweeping wind will get refreshed cause it does so on each crit hit.
2) Positioning, it is vital to position yourself in the midst of mobs, the LTK hits all around so the more mobs you hit, the more likely you'll get a crit and refresh some stacks. Hardest thing is to fight 1 or 2 mobs, like bosses or elites, trick is, try to draw them into crowds of mobs or simply quickly dash to a nearby stack of mobs, hit them a bit to refresh and dash back.
3) Whenever you are attacking just a few mobs, 1 to 3 like bosses and elites, keep 1 eye on the stack counter, if it drops below 3 or 2, simply dash away and give it @5 secs to refresh then dash back in. PS the stacks DO NOT refresh if you are taking damage, so in some instances, when you drop your stacks and you're surrounded by mobs or damage effects, it can be a problem.
It took me some practice but once you master it, believe me, it is the most powerful monk build I have played so far in all of the seasons and good fun too plus super fast if you can kill elites quick enough and dash to the next pack of elites.
Anyways, watch Quinn's video or at least I hope the above pointers will increase your ability to keep the stacks up and enjoy the LTK monk more.
Cheers.