Good posts in here that give good advice, and it's awesome that you're taking the time to look into things, as well as thinking for yourself about your gear. A proactive, and not a reactive approach to tanking is what you need to be successful. I wouldn't really have TPS in mind right now. What you need to focus on before you worry about that is being able to stay alive. You can use the same saying that is used so often for DPS in the case of tanking. How much TPS will you be doing as a corpse on the ground? Doing a bit less TPS inside of kara and heroics generally won't wipe a group. What WILL is when you don't have the stats needed and you get bursted into the ground. Though both honestly end up hand in hand, if an order had to be put to it, staying alive comes first, pushing optimum TPS is secondary.
Tanking heroics is most definitely more difficult than kara. The main difference between the two is the trash, and what you have to deal with it. Inside of kara, as was mentioned before, you will rarely be tanking more than one mob at a time. With CC as well as an OT and MT, outside of a CC or tank dying, the pulls are very controlled. You will be tanking multiple mobs inside of heroics, which means more damage, and there is more opportunity for you to make an error in tanking. With the healing present inside of kara, a stray mob for a few seconds isn't normally the end of the world. In a heroic, if you have a stray mob, it's normally going to be going for your healer, and he's the only one you have. Mistakes inside of a heroic are much more punishing than inside of Kara. All in all however, the two are fairly on par. Kara is basically a big heroic.
As for comments on your gear in particular, I have a few comments on gemming, and a few suggestions for direct upgrades. Drop the STR gems in slots on your gear, and drop the agi gems in your shield. Replace these with stam gems, or at least defense/stam hybrid gems. Ah bought green gems will honestly be fine for the time being, I wouldn't blow your bank on solid stars as most of those items will be replaced fairly quickly. The KoT legs may be worth SoEing up, as they will last you until either badge legs, or Wrynn from Curator. I'll list a few direct upgrades for you, some of which have already been listed.
Shoulders:
Shoulderguards of the Bold. Shadow Labs (Regular) - Murmur (4th Boss)
Chest:
Jade-Skull Breastplate. The Mechanar (Regular) - Nethermancer Sepethrea (2nd Boss)
Weapon:
Grom'tor's Charge. SMV Questline. Begins with
Enraged Spirits of Fire and Earth.
Shield:
Crest of the Sha'tar. Sha'tar exalted. You'll get lots of rep from arc and mech runs for other gear.
Boots:
Ironsole Clompers. Hellfire Ramparts (Regular) - Vazruden's Chest (3rd Boss). I know, I know, it sounds silly, but they're actually REALLY good for going into things initially. You can also do the Mana Tombs escort quest for
Flesh Beast's Metal Greaves.
Ring:
Elementium Band of the Senty. The Arcatraz (Regular) - Harbinger Skyriss (4th Boss)
Trinket:
Adamantite Figurine. Shadow Labyrinth (Regular) - Blackheart the Inciter (2nd Boss)
Gun:
Gyro-Balanced Khorium Destroyer. Takes 375 engineering and a Nether to make, but it's BoE. You can pay the standard price of around 1k for it, or farm the mats out yourself and buy one for whatever the price of a Nether is on your server. I'd suggest farming it, as it's honestly not too harsh on the mats. You're a miner, so you PROBABLY already have some of it on hand.
There's a pretty easy to sort through list of direct upgrades for you. All are aimed specifically at being easily attained solo or by grouping regular instances/quests. Hope it helps.
Edited, Feb 13th 2008 1:51am by FletusSanguine