This is a great site. So far, I've found out what I may have been doing wrong...and what I may have been doing right. I believe I have the mechanics down. Wha't giving me trouble is finding good defense gear for my level 74 Pally. Are there any guides that cover this?
As far as I can tell, no there isn't. People tend to level to 80 as quickly as possible and generally ignore instances as they do.
However, craftables are your answer. Blacksmithing makes alot of lower level defense gear that'll easily push you over defense minimum. Just remember that'll change every time you level up until you hit 80 (where crafted Saronite and Titansteel gear will be your bread and butter while you search for more gear).
At level 74 you only need 510 defense to be capped against mobs 3 levels higher than you. 495 for mobs the same level (do the math) . It'd probably be best to keep with dungeons that are 2 or 3 levels higher than you (e.g drak'tharon: 74-76, and violet hold: 75-77..). Violet hold drops a REALLY nice shield for anyone at level 75, and tank legs as well. I used it until I got leeka's shield in CoT4 regular when I was 79). I was able to tank Violet hold when I was level 73, it was much fun! I had my defense capped to where mobs 4 levels higher than me couldn't crit me. Having some Kara gear helped a bit :P.
Also, since my post I've discovered Kaliban's Class Loot List (Kaliban's Class Loot Lists) which has been updated to include WotLK content. It definitely helped as well. Just in case another "newb" needs pre-80 gear info.