The complaints are harsh engagements and shifts. The scan tool data reveals that there is no amperage command to the EPC solenoid therefor the line pressure is at maximum. There are no transmission codes stored, there are lean codes stored in the ECM. The ABS or the VSC (vehicle stability control) lights may be illuminated. This complaint is prevalent on Chevrolet Silverados with the 5.3 non-flex fuel engine.
The engine is running lean. There are multiple causes for a lean running engine. One of them is an Ethanol-based fuel, E85 in a non-flex fuel vehicle. See the ATSG bulletin “Invalid Engine Torque Signal” for more details about Ethanol-based fuels.
Check the fuel to see if it’s an Ethanol-based fuel (figure 1). Drain the tank and refill with a non-Ethanol base fuel if needed. If the fuel is a non-Ethanol blend then the engine lean codes will require the proper diagnosis and repair.