Both ways. 3 speed was standard on 3/4 ton, but a lot were sold with the optional 4 speed SM420.
With the 3 speed there were 2 transmissions offered. (I'm still looking for the difference)
Below serial number 150-22 19366 was transmission part number 591840.
Serial number 150-22 19366 and above used transmission part number 591875.
'57 GMC 102, Original 347 V8, HydraMatic, 3.08 rear gear, added A/C, disk front brakes, HEI, AFB carb, '98 Honda Black Currant paint. T-boned and totaled 10/12
'52 GMC 152 Stake Bed, Original 228, SM420, added A/C, HEI, disk front brakes, '67 Chev 3.55 rear gear. Gets used as a real truck.
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