I am talking about the end of the sensor ( probe) not the threads. Although you should have left some bear threads to act as a ground too. But on some of the 4R100 castings the probe will hit a casting debri lug on the inside of the case. This will give the readings you are having, most the time if it hots this casting you will break the probe by trying to tighten the probe up. Take a awl and insert it into the hole and measure how deep it will go, then measure it on your probe. I didn't have one of the weird casting cases, but I still used a couple washers to space it more in the center of the fluid flow anyway. I hope this makes more sense. If you have any more ? just PM me as I don't get back on the forums as often as I would like lately.
God Bless
NCH