B&M Transpak - GM TH350C (Lockup)The B&M Transpak is the next step up from the B&M Shift Improver kit. It has all the features in the Shift Improver kit, plus it provides additional driver manual control (GM TH 400, 350, Ford C 6 and Chrysler Torqueflite only). B&M Transpak kit for 1980 1986 GM TH350C (Lockup) automatic transmissions. Most stock automatic transmissions won't downshift into low gear above 15 mph, and automatically upshift at a predetermined speed no matter what gear