Bought a heavier duty Borg Warner solenoid unit and new transducer and installed them yesterday...problem solved (along with a weird "hesitation" on initial acceleration). Trans is now working perfectly! Thanks for the help.

1970 Dodge Charger R/T Hemi Orange U-code 4-speed
1971 Jaguar E-Type Series 3 V-12 4-speed 2+2 Signal Red.