When you check the bottom, look for borers. My Kadota was around 6+ feet tall, 1.5-2" caliper, and was taking a long time to put on new growth. When it did, it was pushing out growth from the bottom, which I ALMOST rubbed off since it was in a really nice tree form that I wanted to maintain. Upon closer inspection, I saw the telltale "toothpicks" sticking out near the bottom, and sure enough, all but about four inches was dead. I hacked it off below the holes, and it is growing back quite well now. Good luck with yours!