re: Pet treats

I picked up a couple of "sweet potatoes" so marked in the produce section but the checker rang them up as red yams. Does it make a difference? So I have one of them sliced up and in the oven for two hours @ 200 degrees. They are at this point, still rubbery. I am hoping to get them at the magic window before they turn rock hard. Do yams cook differently? I wish we had a dehydrator, but it looks like they take up a good bit of room and our kitchen is small.