Rearend for a 1993 k1500 dont know how to find out the size

If you call the dealer with the serial number they should be able to tell you ,or if there is a tag on differential any parts store should be able to tell with tag number. Aside from that take diff cover off and measure gears.

Two ways this can be done.
1. in the gove box there is a build sheet a square
piece of paper thats glued on inside with a bunch
of three or four letter codes . call a dealer and they,
tell you which ones tell rearend info.
2. remove rearend cover , you will see veryis gears
count the teeth on the big gear on the left side,
write it down,count the teeth on the gear that comes from the drive shaft,write it down.
you can call dealer or divide the big gear[ring gear]
with the pinion gear the small gear that comes from
the drive shaft.