Those two points are well served in Imp. Disciplines or focused rage, even cruelty if you really want to. Personally I prefer 2/5 shield spec and 3/3 FR with 2 in imp. disciplines.
My block % as a raid tank sucks; like in the realm of 14%, but I like it that way
The DPS your losing adds too may be scrubs and not attacking the proper target, it's also possible your not changing targets and spamming single target threat frequently enough. Personally I macro Triangle (since DBM likes to use skulls) to my charge (using a modifier of course); that way the mob I charge is automatically marked and people tend to attack the target with the icon.