There are lots of gears in your 78 Chevy.
1) What size truck is it?
2) What transmission do you have?
The axle could be anywhere from 3.55:1 to 6.14:1 depending on the size of
the truck and the options ordered.
As for the transmission, there are specs available for just about any
transmission as to the gear ratios involved. I've got an old Pre-SM420 4
Speed in the '46 and was able to find the gear ratios over at The Old Chevy
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