transmission time!!

ok guys, here goes a wild one. i have a 2003 grand prix se with a 3100. I am experiencing the whining noise that picks up and decreases with vehicle speed and is indicative of the drive bearing being on its way out. Also, i seem to have lost 4th gear as i am currently running around 3100-3200 rpm at 70mph. i started looking for a used transaxle to put in it as i know that it is a 4t65-e and then i hit a wall of varying information and not sure if any of it is correct as some of it is conflicting information. apparently i need to know the tag code for my transmission and after some research, i have discovered that the only tag code for my car is a 1RND. where i now get confused is that the "1" is a production year which would lead me to believe that i could get a tranny from another car as early as '01. Conflicting information from another source tells me that i can only use a tranny from an 03 or 04 model. sooooooooo.......can anyone tell me for certain what vehicles the 1RND was used in for certain? or how to identify a 1RND when its possible that the vehicle that it came out of is not known (like already pulled at a junkyard) or simply the vehicle VIN is not available. i know this swap is a fair amount of work and really dont want to have to do it more than once! as a side note, how difficult is it to rebuild?