Another thing is the 6L90E is better than the 6L80E. One extra clutch per clutch pack, it is 35MMs longer than an 80E, strengthened input and output shaft with wider gears. 2500HD and 3500HD get the 6L90E and don't suffer the problems people encounter with the 6L80E in half tons. Heat failures and torque converter issues due to AFM causing the torque converter to go in and out of lock up.
The 90E first gear is 4.030 vs the 80Es 2.482. That was a huge improvement. 4th gear is 1 to 1 in the 90E and the 80E is 3rd. It diffidently improved the usability of the 6.0 for towing.
I have one of each at home. The 90E is in my truck. The 80E is in my 2014 Caprice PPV (never in police service) The 80E is behind a 400RWHP/400FT/LBS of torque 6.0.