How do I understand ECU/ECM part numbers?

[spakack]

I have recently been looking into my truck problem and I need your guys help. I'm looking on the net and there are a lot of sources for used computers out there. I have been looking on Ebay and found out that there are tons of computer types. Can anybody out there direct me to a page that breaks down how to understand the label on the computer itself. I can find ones for sale that match my truck but the label on the computer is not 100% exact.

For example I found one with part number XL5F-12A650-PD but mine reads the same but with LE on the end. I'm waiting to hear back from them to see if its an automatic or not. I just wish I could find a site that could help me understand the label...