Hate to say it but hills are the tandems bugbear.Until the team works together, you will probably find that one of you is putting in more effort than the other. This will make that rider tire a bit sooner, so the other one then has to compensate. Don't worry though as when the team get together, you will be able to keep up with the pack. Problem is, this may a little while to achieve but do not give up yet.
Depends on the type of bike you have, but "Honking" does not get you too far on a Tandem. Effort seems to go everywhere except the rear wheel

Mind you, when you do become an accomplished team, the hills do not get any easier, they just appear to be shorter, and faster.