I have a 3pally 2dk team at 75 and they seem to hold well enough in instances. The pallys spec ret and use divine storm alot, may be obvious but also talent into The Art of War. If you are critting alot you should almost always have 2-3 insta-cast Flash of light spells ready to spam the tank. When thats not enough I have set up 2 paladins with specific macros to alternate Flash and Holy Light. Forgive me if this is terribly obvious :P