I posted a few days ago and didn't get much interest under "diagnosis please". Let me try again, maybe the title change will help. Under load the trans behaves normally, as soon as I unload the transmission a loud growling noise begins. Between shifts this also is noticeable. This started last weekend with a loud bang cruising up a slight grade at 60MPH. Am I on borrowed time? Thanks

 

Mine used to sound fine under load but would bang when you let off. I tore it apart and the countershaft bearings were toast. Drain the oil out into a clean container and see how much debris is in it. That should tell you if you have something failing. I would say this is something you would want to address as soon as you can.