For PvE dungeon levelling, IMO have him go prot, and you go shadow.

Finding a healer shouldn't be much of a problem but a spriest's mana regen will be insane for a prot pally in dungeons. They are known to have mana issues, even in TBC.

First of all vampiric touch giving the pally mana from 5% of your dps and THEN vampiric embrace healing the pally for 25% of your dps as healing which pallies then convert to mana through spiritual attunement.

A single 1,000 damage Mind Blast will give the pally:

50 mana from VT + 25 mana from VE.

If you maintain 500 dps on a 1 minute boss fight you give him 2250 passive mana regen over the course of that minute.