Dumb question about playing with friends at lower levels.

So I had a couple false starts with characters in 2004 and 2007, but I'm back and going full steam now. The main reason is because I now play with a friend. However, we tried questing together. Progress seemed much slower than when questing alone, and in most cases quests could not be shared. We do dungeon finder almost exclusively now as we both have something to do and get good XP.

He is a human 36-ish holy priest, and I am a nelf 36-ish feral druid. I mostly do DPS in cat form, but have tanked in bear form when needed (like when the tank fucking splits on us). The idea was to level these characters together and work on alts when we aren't playing at the same time. We want to keep their levels fairly close. My "alt" which is probably my main in reality, is a level 50 draenei fire mage, so clearly I've been leveling faster when working alone.

What can we do besides dungeon finder at this point?

Edit: One thing I was thinking of would be to go to zones slightly higher in level then where we should be and just kill mobs since I can tank and he can heal.

Update: Thank you all for the advice. We were able to share quests in a new zone. It was a nice change of pace and scenery, plus we made good progress. Western Plaguelands was a bit meh, but we'll be heading to EP next time we play. I also plan to try tanking with the Druid more.