1965-1987 GM TH400, TH375 & TH475 Automatic Transmissions.The B&M Shift Improver kits feature two options to recalibrating your 1965 1987 GM TH400, TH375 and TH475 automatic transmissions. First is the HEAVY DUTY set up, giving you firm positive shifts without loss of driver comfort for improved performance in all street vehicles. This is a great option for performance street driving or towing. The second is our STREET STRIP set up. Be warned, this will deliver firm positive shifts you will feel, along with