We have a Chinese Pistace that is 6 years old. It has never really grown and now has a couple dead branches with foilage on the lower limb below the dead part. I have been doing some investigation and dug down (carefully) about 6 inches to find a mess of roots which are tangled around each other and cutting into the trunk. I assume that this is a result of being buried too deep but am not sure and don't want to fatally wound the tree by guessing. Any help would be greatly appreciated. I am not sure how to post pics but will post some as soon as I do.

Yeah, it sounds like the tree was planted too deep and has root problems. It also sounds like it has experienced some die-back, which isn't all that uncommon if the specimen was large (3" caliper) when planted.