I've searched google and came up with multiple answers but none that I'm 100% comfortable with.
So my questions is this... I've got a 2003 Sierra with a bad trans. I know all the 4l60e transmissions will bolt up but are they all the same internally?
I've found some answers saying the 99-02 are the different than 03+ so I'm wondering if I need to find a 2003 specifically or if 03+ will work. I found an 04 that was pulled from a Tahoe for a reasonable price but I don't want to get it if it's not going to work.

 

Any '98-'07 4L60E/4L65E/4L70E from an LS-engine donor 2WD vehicle (except C5 Vette) will have a 300mm input shaft and work perfectly. The '03 does have a few strengthen parts (e. g. heat treated sunshell) and therefore later years are better.
An '08 is probably OK, but '09+ are electrically incompatible.
A '04 from another vehicle would be perfect.

 

Well the 04 I bought was no good either. So another question... will one from a v6 work or what is different about them?
Reason I ask is because I've got a friend that has one laying around and he may just let me have it.

 

If it has the 300mm input shaft, indicated by a bolt hole at 12 O'Clock on the bell housing, you are good to go.
What was wrong with the '04?

 

The same crap as the other one. It shifts into 2nd just fine and I feel the shift into 3rd but it just revs. I took it to have it scanned and there isn't a single code, engine or trans. So I assume it's those pesky 3-4 clutches.