Less treasure cards in Dungeon! board game
The number of treasure cards is equal to the number of rooms that exist on each level.  You only get treasure when defeating a monster or triggering a trap in a room.  Therefore, it should never be possible to run out of treasure cards.  My guess is that you were mistakenly awarding treasure in chambers, which should not be the case.  

From the rules:

"Monsters in Rooms have treasure; those in Chambers do not."