During my many attempts tanking Titan HM, there were a couple times where I found myself running out of TP due to how long the fight is.

Using an ability at every chance you get as soon as your GCD is up will deplete your TP, however, once threat is well established, if you just hold off like .5-1 or 2 more seconds between abilities, you will regen TP more quickly than you're using it.

This should prevent you from ever running into a situation where you need to spam them as quickly as possible to re-establish threat but can't because of no TP.