As a couple other folks have said, it seems like your tank is a bit weak in gear. When I hit 70, I was a bit over 10k health with 460+ defense, etc just from quest rewards. As a prot pally, you should be stacking defense, stamina and strength. 490 defense is the cap at 70 to be uncrittable. Stamina is obvious. Strength helps for shield block amount and for increasing your attack power, which in turn makes you do more damage and generate more aggro. After the 3.0.x patch, all pally damage abilities scale with BOTH attack power and spell damage. Don't forget to enchant and gem all your gear. It helps a lot.