I have a 2002 Denali and I've decided to go with the 4L80E. I read somewhere that I will need a crank spacer behind my 6.0 unless I have a 99-00 motor. This is the quote : "You will need the crank spacer for anything except a 99-00 6.0 motor" Is this true?

 

Its correct. 2000 and earlier motors had longer crank shaft and had no need for the spacer. Now on an 01+ you will need the spacer/bolt kit and flywheel for an 80E. Speed Engineering sells it cheap.

 

I have a 1996 Chevy Suburban 1500 4x4 and I put a 4l80e in it and wondering do I need a spacer for the flex plate or is that only for ls only .

 

That's only for the LS. I'm assuming you are also replacing the flex plate? The 4L60e torque converter has 3 bolts vs 6 for the 4L80e torque converter.

Are you also swapping the input shaft of your transfer case to fit the 4L80e?

Edit: Ho-Lee batman, this is a really old thread revival!

 

it's also incomplete in that this caveat additionally applied to a handful of 99-00 4.8s, too.