The first letter of the transmission serial number is the model year designation. For the 4-speeds, U=1951, V=1952. The second letter tells both the series of truck in which it was installed and at which plant it was built. For the second letter, K,L,M are for the RPO 4-speed used in the 3100 and 3600 trucks, D,E,F are for the standard 4-speed used in the 3800 trucks, and N,O,P are for the standard 4-speed used in the 4000 and 6000 series trucks. The build sequence number starts at 1001 for each prefix.
