Not sure but it could be one of those or one of many other things. Maybe one of the Tranny guys will chime in soon. Hope you get it fixed soon. May be time for a 4L80?
[07 Black 3SS ; Maggie 2300, Built 4L85e w/Trans Cooler, SW Hdrs w/True SW Duals, CAI, LS1 Efans, Custom Seat Inlays & Dash Bezel, D&S Rtrs, Keystone Hood, 3 Gauge Pillar Pod, Lowered, Pioneer DVD, Tinted Bermuda Tails, PCMforLess Dyno Tune and much more.