well depending on the phase of the moon and the migratory pattern of the african swallow when your truck was built it could be 3.73s or 4.10s as the most common, but not leaving out 3.45s either, although those were mostly phased out by about 97ish or so... the easiest way to tell is to look at the axle tag on the rear axle as it will tell you the exact ratio on it.
Okay, I knew it was something that involved code language, just didn't know where to look. I'll look after I get out of school. That's wierd because my Z28's stock rearend ratio was 2.73 airplane gears (now 4.56) whereas my truck is probably a 4.10 or 3.73! (But that's to compensate for the low HP right?)