Niobrarafun--
Yours is likely a 3.90 ratio. All the 1/2 ton's I've been around have the 3.90. I've had my 57 since 1968. Put a 63 1/2 ton C-10 rear with limited slip in it about 1977--It had 3.73 ratio & that made it a bit more hiway friendly.. Just my 2 cents! delkydave in wyo