I pulled the engine and tranny out. I got service paperwork when I bought the truck. The tranny was rebuilt by aamco in 2008 at 45,000 miles. The truck only has 52,000 now. The heads, valves, and pushrods are all good. There is a little verticle scoring in the cylinders but almost no ridge. A couple lobes on the cam look a little worn. The timing chain has some slack but I don't think that's the problem. Maybe the knock is a bent rod but they look ok from underneath. I guess I will check the rods and bearings next. I have no experience with this but hoping I can figure it out. Thanks FABO for any advice.