I've noticed recently there has been a very bad change in how people are playing. When I leveled Mage, every group I got into save a few fringe ones, was spectacular. Now my Priest is 79 and it is a nightmare. The worst thing(aside 500dps Feral Druids and DKs) are the Paladin tanks.
1: Not def capped.
I personally do not know the cap for reg dungeons(535 is heroic) but 400 is NOT OK
2: Seal of Wisdom/Light/Justice
NO, NO, NO. Seal of Vengeance is not a hard concept. USE IT.
3: Not using Divine Plea.
.... I don't even know what to say aside, USE IT.
4: Not talenting into Seals of the Pure. At 80 for raids some people argue this. At anything BEFORE 80 this is not debatable. With how bad DPS is until 80, every bit is needed. Do it.
I dunno what is going on but please, PLEASE if you intend to play Paladin read the F.A.Qs.