I'd never tanked before and jumped straight into Gunbreaker because it looked like the most fun...and it has been once I changed into a "humble but yolo" mindset.

-I start almost every run with a macro that says "new to tanking, patience and tips appreciated!". I occasionally get good advice and often get a "you got this!" type message and anxiety fades. -I go wall-to-wall with a big smile in my face. 10% of the runs I mega die so I pull less next time, 20% of the runs I barely die and I ask the healer if I should back off (usually the answer is no), 30% of the time I get a "hell yeah!!" because people don't expect the new guy to go all out, and the rest we just cruise. -IMO, groups would rather have some excitement and occasionally wipe on trash than go slow. Don't be afraid to die!! I listen to feedback and haven't yet had anyone be pissy at the end of a run. -As long as you are geared it is hard to die on most bosses (ex savage) as a tank. Sounds like you know the mechanics so bosses should be a piece of cake.