I have a 55 1ST with a 390 diff. I am thinking about changing the ring and pinion . Was there any options 373 ?

The 1955 1st design truck shares the differential parts with the 1955 2nd design trucks.
The choices in 1955 was a 4.11 and a 3.90.
Jim Carter sells a 3.38 ring gear and pinion for a high speed replacement.
From 1959 and up Chevrolet offered a 3.38 ratio as an economy option.

http://www.jalopyjournal.com/forum/...-ton-truck-3-38-1-highway-gears.1013374/

That is the lowest price I have seen.

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