the people talking to you are full of it
I've tanked plenty of t5 content and don't have problems even though i have less avoidance than you. When I need to stack more avoidance I can put it up to 51% total avoidance, but I rarely find stuff that needs that much. You're HP is solid, armor is pretty good, and the guys telling you otherwise are just retarded, they're making assumptions that "guides" aren't right when in fact they have more basis for truth than their "healers' speculation".
I think your best bet is just to find a guild that understands tanking better. Even if you regemmed for this guild, and geared yourself the way they wanted you to, You'd be miserable because they'd be telling you how to play your class when you're the one who's done the research.