For what it's worth, my Dad has an '02 with the 8.1 & the Allison transmission.
It's a strong engine, no doubt. However, the transmission is loud, whiny, and clunky.
I'm not a fan, for that reason. He's carried it to the dealer & to a transmission shop, and they have told him it is "normal."
I don't buy it, and am not a fan...
Just my $0.02.
scott