Your tranny is a freak for sure. Some guys like you get lucky, and they hold together. Some guys like me (twice), my brother, CrazyLT1, anniversaryss, etc…have problems. Most performance transmission shops will NOT even attempt to build a 4L60. There are only a few good shops in the country that build 4L’s strong enough to run 10’s consistently and they aren’t cheap. Th350/400 FTW!