TRANSMISSION 723.6 in MODEL 957 with CODE (GB1) Allison WT MD3060 automatic transmission with retarder, 6-speed TRANSMISSION 723.6 in MODEL 970, 976 with CODE (GB8) Allison WT MD3060 automatic transmission with retarder, 5-speed TRANSMISSION 723.6 in MODEL 950, 952, 957 with CODE (GB8) Allison WT MD3060 automatic transmission with retarder, 5-speed TRANSMISSION 723.6 in MODEL 957 with CODE (GG4) Allison WT MD3066 automatic transmission with retarder, 6-speedar2719w0222a