Consider the Cold Iron Vanquisher instead of the Leviathan path. They're both great in their special little way, but damage against undead will help a lot.. and undead mobs in Tier 3 are really dangerous (people quit parties all the time because of graveyard, and there is always Vanaduke).

Looks like someone's not been paying attention to the hundreds of posts about how awful CIV is. Worse in every single way.

Seconding the suggestion of using an Owlite series shield, as the Shock resist will definitely come in handy.

Owlite is a great all-purpose shield, plus going Vog will make your slow swords a little faster.

I'd recommend getting Flourish > Final Flourish line for dealing with Wolvers, Greavers and Devilites. These are all a pain to fight in T3, regardless, and Flourish has a very fast interrupt rate that pretty much leaves your target helpless until its dead. Only equip it when you know you're going to need it more than something else, however! (e.g. upcoming strata has a lot of Beasts and Fiends)

Ignore Cold Iron series, lol. If you want a faster sword that Undead are weak to, go with a fire or ice Brandish, but given you have Avenger and Silversix there's really no point in getting yet another weapon for undead.

Ascended Calibur would be a nice alternate to your Sealed swords due to faster attack speed, although as DragnHntr said, Swing > Shield is a great way to play it safe and take a lot less damage in T3, especially when you're in a group. (More chaos, harder to kill a single target before it harms you, etc.)

For me, I'm finding that I like playing to mob weaknesses. When solo, I stopped equipping my Leviathan and use the Brandish series (shadow & ice) and Flourish instead. This requires a lot of weapon switching, but lets me mow down a single target quickly. It's fun, aggressive play, but obviously more risky than swing > shield. Leviathan has more reach and is probably smarter for group play, however.

I'm having a lot of success even with the Brandishes and Flourish only at 4* -- I've cleared to the Core several times with only swords equipped too, so bombs/guns aren't a requirement, just a play style/preference.

Beyond that, check the gatemap before entering... do you have a weak spot for what you're about to encounter? (e.g. shock strata blow goats) Try picking a gate with critters in it you know you're effective against. Doing this will make your trips into T3 more fun, BEFORE you get any more gear!

Yeah go with a Leviathan instead of a CIV. You should be carrying a Divine Avenger as well, and that will cover your needs against the Undead.

I roll with Leviathan, Divine Avenger, Gran Faust, and Argent Peacemaker. The Gran Faust is basically there for Gremlins.