Transmission Shifting Hard
(First Owner) I have GMC Sierra 2006 2500hd 6.0L
4 speed automatic transmission with mileage
290000km. When I start the engine everything work
fine until I cross 120 km/h the problem start here,
the transmission start shifting hard from gear 1 to 4.
And this problem disappears when I restart the car.
When I drive slow this issue not happening!
Most likely a live data scan is going to have to be performed to see what is going on, could be a number of things, TCM, speed sensor, shift solenoids or even transmission internal pressures.
I have same situation and I'm from dxb dubai but my chevy truck have 6.2l l94 with cam stage2 and intake mainfold ls3 but i dont know what is the problem even the tuner