My 2001 Impala was getting a code 1811, it was shifting irregular and banging when put into reverse.
As per a previous post from another member the code was a PCS-pressure control solenoid problem.
My friend does transmissions, so he was able to repair with out pulling the trans out and replaced the PCS, another solenoid for the lock-up convertor and installed a fix type shift kit adjuster in the valve body.
My friend said this is a very common probelm for this transmission.
The car has not shifted this nice in over two years!
Thanks to the forum members who led me to this fix.
ronvb