Seed/Key algo

I'm hoping somebody here might be able to help with this.

Is there any software that can find the combo between a seed and key?

General Motors uses a seed/key to unlock the their engine controllers to allow for programming. While I have been able to hack the code, nobody is able to figure out what the seed/key
combo is.

The seed and key is stored in the ECM.
It is not calculated by the ECM, only the returned key is checked for a match. The scan tool (TechII) made for GM does the calculation when it gets the seed from the ECM (engine controller).

I have been able to get several seed/key combos by removing and reading the flash chip contents.

How do I tackle this this?

Thanks.