I got the black mushroom and leoric's bone (forgot the exact name) within an hour, without problems.
Having a witch doctor set with manajuma/angry chicken and illusonary boots really helps
Same problem as other people for the gem. Sometimes, but not always, it teleports to town once level 2 reached.
At first I thought it was because it somehow knew that Chiltara wasn't there, but several times I stopped it when it tried to teleport and went to check if that was really the case, but no. Chiltara was there.
Also, I read somewhere that when RoS came out, Blizzard made changes so Chiltara would spawn more often, but in counterpart, the gem droprate has been lowered.