This is the way I understand it based on posts from this site and and a few other sources....
though I don't guarantee it is all correct.
The plain old stock 3/4 with stick would be a 4.57 ratio.
The 4.10 is found in 3/4 ton trucks with coil springs and auto transmission.
The 3.90 was found in the 3/4 ton suburban with automatic, but not all of them and is quite rare from what I understand and most have never even seen one.
