This site will tell you what your VIN means, and it also tells you what NUMBERS or LETTERS can be used if its wrong. Very good info.

VIN Decoder

Leave the VIN Box Blank and hit submit to figure out what the codes mean, then next to the meaning there will be a small link that says "more info" click on this to figure out what characters can be used in that area of the VIN. This can be handy to fix a error in your VIN, or just figure out a tad bit more about your truck and see if the last owner changed anything.

 

This is great info! I will post this in the FAQ! Thanks!