1977 K10 4x4 , LM7/4L60e/ NP241c ..Received a call from my tuner..The transmission was acting really odd. It would go for a bit then go into neutral and not move forward or back. Topped fluid off before tuning. Not sure if we have a sensor miscommunication or what. Going to scan it today and see if he can come up with some idea…Anyone ever had this issue ..??

 

Now this one I HAVE NO IDEA HOW TO RESPOND TOO LOL

Actually I do Im in dark mode and the words dont show, Drop pan sounds like filter is clogged. Most likely converter failure on dyno would be my guess.

 

Yeah this sounds like a sudden loss of fluid pressure. Put a pressure gauge on the trans; the pressure port is on the driver's side.
Short of a catastrophic internal failure and assuming the shift linkage is correct, you only need fluid pressure for Reverse to work. The trans connector can be disconnected and you still will have Reverse (and likely 3rd gear).