[Captain J]

Greetings to all,
Sorry for late response. I was sick (corona or flu) not sure.
Again, trans oil is new and clean, drove it less than 200km since last oil & filter change, all GM products. No silicone inside the governor housing. When replacing the old filter, I made sure the old o-ring is removed, the new o-ring was lubricated with trans oil, then it was fitted in the filter neck, then it was placed inside the housing. Truck drivers normally.

Update 12/23/2023 8:30pm my time.
I cleaned the governor tested the valve it works fine, made a gasket from gasket paper, put it back, added new oil to replace the spilled oil. Drove the truck, no change, it will not shift.
I’ll try to fish the valve body behind the vacuum modulator, and see.
Otherwise I’m out of ideas.