Unless this VIN # is a secret, there's not much we can tell you.
On a '55 Chevy, the VIN # tells you only the following:
Series of the truck
The year of the truck
The assembly plant
the production number sequence
That's it. It doesn't tell you whether you have a 3 speed or not. Don't know where you got that idea from, but it's not so.
There are codes on the transmission and the axle and there may be a data plate on the firewall, for additional info.
If you can dig up all these numbers, post them and we'll tell you what we know.