Quit "Stalling" ( 'Roll' Reversal )

Did you check and adjust the rear band when you serviced it last summer? If not it's possible it's just the band is worn and not clamping down on the rear drum enough to hold it. Since you didn't mention any problems with any other gear it has to be a problem with the rear band, apply servo, or valve body. If you did adjust the band when it was serviced the next step is to run a pressure test on the rear servo.