Transmissin Rebuild. Which manual?

I am in the process now in purchasing a spare trans for my 2003 lesabre for a rebuild. I have the service manual for the vehicle but does not include any trans rebuild information. I have been looking for what manual to use and have found two.

Helm has a book (part #: GMPT03TURM) and the ATSG has a repair and update manual. From other threads i have heard people recommend the ATSG manual and I have not come across anything on the Helm manual. In the intro or forward in the helm service manual it refers me to use the Helm Transmission/Transaxle/Transfer Case Unit Repair Manual or TURM. Now, i don't know if that has any repair information, or only includes fluid flow and any other internal function information.

Does anyone have any incite in the differences of these books? And if anyone has any experience in using one, or better yet, both of these books, I would be happy to hear any advice or input on what one to purchase.

The ATSG is the industry standard

I agree, ATSG is a Must...