Im tanking for some while now and did not had problems with threat (except on Halfus little dragons I need few seconds)
1) mark them - use macros / key binds / addons, whatever You are comfortable with.
2) DnD, it does pretty much all You need.
3) Death Grip caster (usually skull)
4) Few hits DS and HS spam, if still problems - Blood Tap + HS, RS dump RP, repeat
5) Addon Taunt Master is must - it allows You to taunt off target without trying to find aggroed mob
6) Tidy Plates - Threat Plates - it shows targets attacking You, other group member, other tank, and loosing aggro by different colors so You always are aware of which mob is attacking someone else and who is going to and prevent that before it happens.
Plus check Your expertise rating - should be above 17.
If at first you don't succeed, you are running about average