Wear of the accumulator control bore and valve spool causes low accumulator pressure that results in soft shifts.
Ream the valve bore and install the Sonnax oversized valve, matched spring and oversized end plug.
The 4L80-E accumulator control valve controls shift firmness by managing accumulator back pressure. Wear at the valve or bore can lead to multiple symptoms, the most common being reduced line pressure in reverse, elevated line pressure in drive, and soft or harsh upshifts depending on location and magnitude of wear. When valve/bore wear allows cross-leakage of torque signal/boost oil to exhaust to the sump, line pressure drops causing soft shifts. Alternatively, when bore wear allows drive oil to enter the torque signal passage, line pressure increases and shift feel hardens.
Contact a Sonnax Parts Distributor.
A vacuum test fails to yield the indicated 14 or 18 in-hg or greater, depending on the port tested as shown, or if visual wear is detected.