I have a lvl 85 pally tank and he has good gear and all but the bad thing is he doesn't have a lot of hit and expertise and because of that i keep missing and losing aggro. But i've seen a lot of tanks mostly have gear with mastery parry and dodge and not so much hit and expertise. And last i checked mastery was a really important stat for tanks but the drawback to that is you don't have a lot of hit or expertise and therefore you will miss most of the time and lose aggro and that's what's happening to me. if anyone here understands my question please help.

Simple answer; yes. Hit and expertise is just important to a DPS as it is to a tank, if you don't have them - like you apparently don't - you will keep missing and dropping aggro.

Parry/Dodge/Stam/Mastery is mostly used by tanks whom -have- already achieved getting their hit and expertise up to par.