Sudden issue holding aggro

For context, i play guardian. Currently ilvl 231ish.

I have ***never*** had aggro issues. Not in S1, not so far in S2. Yet as of this reset i keep losing aggro. CONSTANTLY.

i'm pressing the same buttons i always press. using the same CD's at the same points. And yet today alone (2 dungeons) i can count 7 deaths due to lost aggro. If not for my quick reactions and some seriously good healers, it would be a ***lot*** more.

And i'm not talking "DPS hit a CD before i had built threat" loss of aggro here. i'm talking "DPS used normal rotation" or "trash is half dead and DPS hit a CD" loss of aggro

Am i going mad? Is it due to my 1 vault item (my own fault i know) putting me 5-7 ilvl below the DPS? Am i the only one noticing this? Whilst i'm clearing 15/16's fine, i'm concerned this is going to force me into lower keys where the DPS ain't hitting quite so hard...

*N.B. Before the "whai you play wow still, blizz bad!" starts, my sub isn't renewing. But i'm not just giving them free money. I'm getting my subs worth before moving onto something else until blizzard can demonstrate they have fixed the cesspit too many of them clearly seem to deem an acceptable workplace.*