Hello Sir,
Here are some food for thoughts:
1) 21 or 22 lands
When I'm playing 21 lands in Nic Fit, I'm stretching the manabase like there will be no tomorrow.
Mathematically speaking, this means you can't reasonably play 2 utility lands in here.
When I'm looking at your list, I count 14 G 11 W 11 B.
This is asking for trouble.
Here is the configuration I would prone (Karakas > PT)
14 G 14 B 14 W 21 lands
1 Plains
3 Forest
2 Swamp
4 Verdant catacombs
4 Windswept heath
1 Bayou
1 Savannah
3 Scrubland
1 Taiga
1 Karakas
This gives you everything you would need for casting T1 any G/B/W spell (veteran/cabal/PTE).
Also, you definitely want a T1 fetch -> forest against any unknown opp, opening you up for a T2 Scrub.
I believe this gives you the best operating system since you would be able to cast everything you need with just forest+scrub (at least all CMC<=2 spells).
2) Thragtusk
I feel you have too many high CMC bombs.
When one is playing 4 rhino, I truly believe that Tusk is not needed. This is even more true when you have access to DLD.
This gives you another creature slot.
I'm aware that Painful Truth can sometimes push you very low (lifepoints wise) and you'll have to assess what you better like in the following as I would either play:
+1 DRS
or
+1 Knight of the Reliquary
- DRS will further fix your potential life issue + mana issue. It is also the best PW for 1 mana
- KoTR is a huge GSZable beatstick. We might not have ways to abuse it like Maverick but I've grown very fond of this card. It is also another out to huge demons (fetching Karakas), at instant speed. Its ability to further thin the deck should not be overlooked (as the shuffle effect for top).
The only other bigger beatstick is
Centaur Vinecrasher. But CMC 4 and no ETB trigger/ability is kind of harsh...
3) Sideboard options
Here is your list with a few comments:
2 Canonist
2 Surgical
3 Duress
1 Toxic Deluge -> Golgari Charm feels like a better SB cards. Regen Gaddock/Canonist can be a matter of life or death
2 Carpet -> I don't like those as we are playing DRS and SLG + useless against non blue deck. Nonbo with Deed.
1 Garruk Relentless -> Sorin, lord of Innistrad is a very strong consideration. Stealing Jace / Demons had happened quite often
2 SLG
1 Gaddock
1 Null Rod -> Interesting but as you have no way to cantrip/tutor, it feels like very random
Here is a revamped sideboard proposal:
1 Canonist
1 Thalia -> Canonist n°2 but better in some other MU. Could be protected with Karakas.
1/2 Surgical -> I believe with 2 DRS + 1 Ooze + 2 SLG + 1 Surgical = enough gravehate
3 Duress (I got your point about digital TS)
1 Golgari Charm -> faster than Toxic in the MU you care. Swiss Army knife against others.
1/2 Aven Mindcensor -> I've learnt to respect Da card, such a beating in so many MU + IT DOES trade with delver.
2 SLG
0/1 Gaddock -> I love the card but redundant/nonbo with SLG
0/1 Dryad Militant -> Faster than Gaddock (CMC 1 or GSZ @2) doesn't block SLG and drastically slow down a few MU
1 Sorin, Lord of Innistrad
1/2 Liliana of the Veil (Yes I know 88 Tix...) -> she is just a powerhouse vs combo/control/aggro AND you are playing Painful Truth.
Hope this will give you some ideas...