I searched for this topic and couldn't seem to come up with a clear answer on it...
Haynes finally added the 2004-2007 GPs to the Regal/Lumina/Cutlass/'88 to '03 Grand Prix manual that has been out for years.
Same old GM FWD W-Body book
Now what I was curious about was if the older edition of that manual (without the '03 to '07 GP listed on the cover) would be the same thing? I found one at Half Price Books for $4 today.
If not, wouldn't the '95 to '05 Impala/Monte Carlo be a good Haynes manual to pick up? I was always under the impression the '04 to '07 GP could be thought of as a "4-Door Monte" and both the Impala and Monte use the 3800 engine. It just seems to me the electronic info from the first book with the '04-'07 GP listed might be out of date compared to the more modern '95 to '05 Impala book.
See it here: Impala/Monte Haynes book