Nooooooooo!!!! There is a change in 2004. Yes, 4l60E, but the website is correct. There are whole slew of changes in 2004 that does not meet the eye. You have to do a VIN check, but I wanted to move my new Tranny from 2000 to my 2004. Should have been a piece of cake. Worked on a 2003, not the 2004.
those changes are internal to the transmission and do not effect its interchangeability. i spend the better part of 2 years dealing with issues with my wifes 04 GTO that came with a 4l60e and did plenty of research. the 65 got the 5 planetary rear gearset and a stronger shell and slightly better clutches and bands. otherwise its nearly identical inside and 100% identical outside. they may have also changed the stall speed on the converter, but the physical converter size/mounts etc are all the same. as i said earlier you may have to switch the PRND indicator between the transmissions as that part IS different between the years/cars/trucks etc but only because of the connectors, its mounting and mechanism are the same.
there is NO physical difference in 1998+ 4l60/65/70e transmissions as long as they are all 2wd. i have two of them in my garage right now. one is the 60 that came out of my wifes GTO and the other is the one out of the crew cab sierra. 100% identical on the outside. ive switched them between platforms without issue and no cares on the years. GM doesnt care what year 4l60 you turn in as a core, that should say something about the interchangeability of it.
unless you can tell me the exact differences im going to take your post as meaning you paid a shop to do it and are going by what they told you.